From clang@astro.ucla.edu Tue Aug 13 14:56:20 1996 Date: Tue, 13 Aug 1996 11:55:56 -0700 From: clang@astro.ucla.edu (Cornelia Lang UCLA Astronomy) To: gcnews@astro.umd.edu Subject: submit sicklepistol.tex to appear in ApJ, 1 Jan 1997 % below is double space %\documentstyle[12pt,aasms]{article} % below is single space %\documentstyle[aaspp]{article} % below is two column, plus use \twocolumn below %\documentstyle[aaspptwo]{article} % below is another single space %\documentstyle[aasms,tighten]{article} \documentstyle[aasms4]{article} \textwidth 6.5in \def\kms{km s${}^{-1}$} \def\b{$\beta$} \def\a{$\alpha$} \def\ab{$\sim$} \def\yz{Yusef-Zadeh} \def\p{$\pm$} \lefthead{put in names for page header} \righthead{put in abbreviated title for page header} \def\fh{\hbox{$^{\rm h}$}} \def\fd{\hbox{$^{\rm d}$}} \def\fm{\hbox{$^{\rm m}$}} \begin{document} \title{VLA H92\alpha~and H115\beta~Recombination Line \\Observations of the Galactic Center H II Regions: \\The Sickle (G0.18-0.04) and Pistol (G0.15-0.05)} \author{Cornelia C. Lang\altaffilmark{1},W.M. Goss\altaffilmark{2}, D.O.S Wood\altaffilmark{2,3} } \altaffiltext{1}{Vassar College Observatory, Poughkeepsie, NY 12601. Current address: Department of Astronomy, 8979 Math Sciences Building, UCLA, Los Angeles, CA 90095-1562; email: clang@eggneb.astro.ucla.edu} \altaffiltext{2} \altaffiltext{3}{Kodak Scientific Imaging Systems, 4 Science Park, New Haven, CT 06511} \setcounter{footnote}{0} \begin{abstract} The Very Large Array has been used in the CnB and DnC configurations to observe the remarkable Galactic Center sources, the Sickle and Pistol, near $\ell$=0{\fdg}18 b=-0{\fdg}04. These HII regions have an unusual morphology and may be physically associated with the linear non-thermal filaments at $\ell$=0{\fdg}18 which appear to intersect the sources. The H92\alpha~(8.31 GHz) and H115\beta~(8.43 GHz) radio recombination lines arising from these sources have been observed with angular resolutions of 6\arcsec~and 9{\arcsec}, respectively. In addition there is a probable detection of the helium line in the Pistol (Y$^+$\sim14\pm6\%), while in the Sickle, no helium lines were detected with an upper limit of Y$^+$\sim 5\% (3$\sigma$). A complex velocity field has been observed in both sources. The LSR velocity in the Sickle varies from 0 to 75 \kms, with an average velocity of $\sim$35 \kms; the average velocity of the Pistol is $\sim$115 \kms~. The recombination line properties of the Sickle and Pistol (FWHM line widths, line to continuum ratios, \beta~to \alpha~ratio) are consistent with photoionization from hot stars. The \b~to \a~ line ratio of $\sim$0.35\pm0.07 over most of the Sickle and Pistol does not differ significantly from the LTE value of 0.28. The average LTE electron temperature, T$_e^*$, for the Sickle ($\sim$5500 K) is similar to typical Galactic Center HII regions, and T$_e^*$ for the Pistol is somewhat lower ($\sim$3600 K). An additional HII component in the line profiles of three regions of the Sickle in which the non-thermal filaments are present suggests that an interaction between the ionized gas and the non-thermal filaments is occuring. The probable detection of He92\alpha~in the Pistol and the non-detection in the Sickle may be due to a difference in the radiation field of the ionizing sources. \end{abstract} \section{Introduction} One of the most remarkable structures near the Galactic Center is the pair of radio sources, the Sickle (G0.18-0.04) and the Pistol (G0.15-0.05), first imaged with the Very Large Array (VLA) by Yusef-Zadeh, Morris \& Chance (1984). Assuming a distance of 8.5 kpc for all sources in this region, these HII regions are located \ab30 pc north of the Galactic Center and appear to intersect the non-thermal filaments (NTF), the unusually long (30 pc) and narrow ($\lesssim$ 1 pc) structures which are perpendicular in projection to the Galactic plane at $\ell$=0\fdg18. The Sickle extends over $\sim$3\arcmin~(7~pc) and consists of two main portions which are nearly perpendicular. The continuum and line emission along the length of the Sickle is quite irregular. The Pistol is a more compact source with a linear extent of \ab0\farcm6 (1.3 pc), located \ab1\arcmin~(2.5 pc) to the SE at nearly the center of curvature of the Sickle. The unusual morphology of these HII regions may, in part, arise from their apparent intersection with the NTF. There have been a number of detailed studies of the sources at $\ell$=0\fdg18, b=-0\fdg04. Two of the single dish studies of the H85\a~and H109\a~recombination lines at the Galactic Center (Pauls, Downes, Mezger, \& Churchwell 1976; Pauls \& Mezger 1980) show the Sickle to have a positive LSR velocity, \ab 40 \kms. Using the Green Bank 43m telescope, Anantharamaiah \& Yusef-Zadeh (1989) observed the Sgr A region which included the Sickle and Pistol and Arched Filaments using the H78\a, H91\a, and H98\b~recombination lines. The radio structures near the Galactic Center were imaged using the VLA in the B, BnC, and CnD configurations at 6 and 20 cm with resolutions of $\sim$3\arcsec~and \ab5\arcsec~by Yusef-Zadeh \& Morris (1987a). Images of the regions in this field where the NTF appears to intersect the Sickle are discussed by Yusef-Zadeh \& Morris (1987b). Detailed VLA recombination line observations of the Sickle were carried out by Yusef-Zadeh, Morris, \& van Gorkom (1987) using the H110\a~transition in the DnC configuration with a resolution of 14\arcsec. The velocity of the Sickle was found to lie between 30-50 \kms, with line widths \ab20 \kms. The Pistol was discovered as a broad line at the edge of the observed velocity range (V$_{LSR}$ $>$ 110 \kms). Subsequent H92\a~observations with an extended velocity coverage were made with a resolution of 20\arcsec~x 10\arcsec~by Yusef-Zadeh, Morris, \& van Gorkom (1989) using the VLA in the D configuration. These observations found that the Pistol has V$_{LSR}$ \ab 120 \kms~and a FWHM line width \ab60 \kms. The main issues raised by these earlier observations were: (1) the possible physical relation of the Sickle and Pistol with the NTF and (2) the source of ionization of these HII regions. Yusef-Zadeh \& Morris (1987b) suggested that the Sickle and Pistol are collisionally ionized by interaction with either the relativistic gas or the magnetic field associated with the NTF. CS J=3-2 observations (Serabyn \& G\"{u}sten 1991) reveal that a molecular cloud at V$_{LSR}$=25 \kms~may be physically associated with the Sickle, but not the Pistol. Based on the agreement in velocities between the ionized and molecular gas, they suggest that the Sickle is the leading edge of this molecular cloud which is ionized by the Alfven Critical Ionization Velocity (CIV) effect (Morris \& Yusef-Zadeh 1989, Serabyn \& G\"{u}sten 1991). According to the CIV model, the ionization of a neutral cloud occurs as it enters a region of magnetic field - the magnetic fields associated with the NTF. As the edge of the cloud moves into the magnetic region it is stopped and ionized by collisions between the neutrals and existing ions which spiral around the magnetic field lines. This effect is further discussed with respect to the Galactic Center by Nicholls (1992), and with respect to the Arched Filaments by Morris \& Yusef-Zadeh (1989). Subsequent high resolution molecular (CS J=2-1) observations (Serabyn \& Morris 1994) over three regions of the Sickle reveal a close connection between the NTF and the molecular gas. These observations show that the clumps of emission in the molecular gas coincide with apparent discontinuities of the NTF at the positions in the ionized gas where the NTF are present. Serabyn \& Morris (1994) argue that these locations are sites of the acceleration of relativistic particles along the magnetic field lines, and that magnetic reconnection may occur at these endpoints. A continuum feature has been observed near Sgr C (Liszt \& Spiker 1995) which is similar to the Sickle: a shell-like HII region associated with a non-thermal filament at $\ell$=359\fdg4, b=0\fdg006. The brightness of this unusually-shaped HII region changes as a non-thermal structure apparently passes through it, as is the case in the Sickle/NTF association (Yusef-Zadeh \& Morris 1987b). Earlier models for ionization of the Sickle and Pistol favored shock or collisional ionization (e.g. CIV effect), while UV photoionization was considered a less likely mechanism, due primarily to the lack of ionizing sources. However, studies in the near-infrared (Okuda et al. 1990; Nagata et al. 1990) detected a cluster of stars called the Quintuplet, located 10-20\arcsec~N of the Pistol. Deeper infrared observations near the Quintuplet reveal a number of much hotter Br$\gamma$ and He I emission line stars (Moneti, Glass, \& Moorwood 1991; Harris et al. 1994; Cotera et al. 1995; Figer et al. 1995). Several of these stars have been classified as Wolf Rayet stars (WC and WN type), in addition to the identification of a possible Luminous Blue Variable (LBV) (Figer et al. 1995). Both Cotera et al. (1995) and Figer et al. (1995) suggest that this star may be responsible for the ionization of the Pistol, located at the center of curvature of this source. In this paper we present new VLA images of the H92\a~and H115\b~radio recombination lines of the thermal sources near $\ell$=0\fdg18, b=0\fdg00 with resolutions of \ab6\arcsec~and \ab9\arcsec, respectively. The major goal of this recombination line study is to image the complex velocity field of the Sickle and Pistol, to use the \b~to \a~line ratio to examine the nature of the ionization based on possible non-LTE effects, and to investigate possible interactions of the Sickle and Pistol with the NTF. The observations and data are described in sections 2 and 3; discussions of the velocity field, the \b~to \a~ratio, interaction between the thermal gas and the NTF, and their sources of ionization are presented in section 4, with the main conclusions summarized in section 6. Figure 1 is a schematic representation of the sources which are discussed in this paper. With a primary beam width of 5\farcm4 the Sickle (the prominent source at the center), the compact Pistol to the SE, and portions of the NTF perpendicular to the Galactic plane at $\ell$=0\fdg18 have been observed. The compact sources O1 and N3, previously observed by Yusef-Zadeh (1986) and Yusef-Zadeh \& Morris (1987b) are indicated, in addition to the Quintuplet cluster (the cross to the NE of the Pistol) and the LBV candidate (S of the Pistol). \section{Observations and Reductions} Two configurations of VLA were used to image the field near $\ell$=0\fdg18. The parameters for the H92\a~and H115\b~observations are summarized in Table 1. Line images were made at a number of resolutions, and the image parameters are presented in Table 2. For the H92\a~line data it was necessary to smooth the images to a resolution of \ab6\arcsec~in order to detect the weak recombination lines with typical line to continuum ratios of $\sim$0.1. The ``high'' resolution data refer to the naturally weighted CnB and DnC H92\a~observations (\ab6\arcsec~resolution) while the ``low'' resolution data refer to the DnC H115\b~observations (\ab9\arcsec). In addition, the H92\a~observations were convolved to this lower resolution in order to compare with the H115\b~observations. Line free channels were used to determine the continuum. The continuum subtraction was carried out in the uv plane using the AIPS task UVLIN (Cornwell et al. 1992). The profile analysis was carried out using GIPSY, the Groningen Image Processing System (van der Hulst et al. 1992). Spatially integrated, continuum weighted H92\a~and H115\b~line profiles were made and Gaussian functions were fitted to the profiles. The singly ionized helium abundance, Y$^+$, is calculated from the ratio of the integrated line profiles of the helium and hydrogen lines. For regions with no detectable helium, an upper limit is estimated. \section{Results} \subsection{Continuum} The uniformly weighted continuum image of the Sickle and Pistol is shown at a resolution of 2\farcs0 x 1\farcs7 (PA=59\arcdeg) with rms noise of 0.2 mJy/beam in Figure 2 (Plate 1). The continuum contours are based on the ``high'' resolution (6\arcsec~resolution) data of the same region are shown in Figure 3. The numerous knot-like regions of emission are evident along both extents of the Sickle in both figures. The emission surrounding the Pistol, which has the striking form of a rectangle, appears to be 'confined' between two filaments of the NTF, similar to the 6 cm observations of Yusef-Zadeh \& Morris (1987b). The 8.3 GHz continuum parameters for several point sources, N1, N3, and O1 (Yusef-Zadeh 1986, Yusef-Zadeh \& Morris 1987a) also observed in this field are listed in Table 3. The quantities derived from the continuum observations for the Sickle, Pistol, and O1, are listed in Table 4. The total flux density (S$_\nu$), measured angular size, linear size of the equivalent sphere, electron density (n$_e$), emission measure (EM), mass of ionized hydrogen (M$_{HII}$), number of Lyman continuum ionizing photons, (N$_{Lyc}$), and continuum optical depth ($\tau_c$) are listed. The formulation of Mezger \& Henderson (1967) was used. \subsection{Recombination Lines} Spatially-integrated profiles over the Sickle and the Pistol are shown in Figures 4a-d; the parameters of the Gaussian fits to these profiles are summarized in Table 5. The ten boxes in Figure 5a represent eight regions in the Sickle and two nearby sources for which line profiles were created from the ``low'' resolution data and labelled L1-L10. The four boxes in Figure 5b represent the regions of the Pistol for which profiles were constructed from the ``high'' resolution data and labelled H1-H4. These regions were chosen in order to examine the complex velocity structure over smaller areas and to investigate the properties of the radio recombination lines of the Sickle and the Pistol in regions where the NTF intersect the sources. Figures 6 a-j present the integrated profiles corresponding to the regions in the Sickle and the two additional line sources as shown in Figure 5a; the parameters of the Gaussian fits to these profiles are summarized in Table 6. The four integrated line profiles for the regions of the Pistol shown in Figure 5b are presented in Figures 7 a-d, with the parameters summarized in Table 7. In addition, the GIPSY fitting routine PROFIT was used to fit single component Gaussian functions to the ``high'' resolution data at positions which have S/N $>$ 3 in the H92\a~line. The distribution of H92\a~line amplitude, central line velocity (V$_{LSR}$), line width ($\Delta$V$_{FWHM}$), and \b~to \a~ratio from the Gaussian fits of the H92\a~and H115\b~lines are presented in Figures 8-13. \subsubsection{H92\a~Recombination Lines in the Sickle} The mean H92\a~V$_{LSR}$ of the integrated Sickle profile (Figure 4a) is \ab35 \kms. The He 92\a~line in the Sickle was not detected, with an upper limit, Y$^+$\ab5\% at a 3$\sigma$ level. Values of the V$_{LSR}$ of the eight individual profiles within the Sickle (Figures 6 a-h) are primarily between 0-75 \kms. Three of these regions (L2, L3, L8) have double peaked profiles which have been fitted with two Gaussian components. The line profile for L2 has been fitted with two Gaussians (see Table 6), however, only the major component (V$_{LSR}$\ab47 \kms) is shown in Figure 6b. The components in L2 are separated in velocity by nearly 100 \kms~with V$_1$\ab~-50 \kms~and V$_2$\ab47 \kms. In region L3, the separation between the two components is 53 \kms, with V$_1$\ab~36 \kms~and V$_2$\ab~-17 \kms. The separation in L8 is 47 \kms, with V$_1$\ab~53 \kms~and V$_2$\ab~6 \kms. The $V_{LSR}$ varies dramatically across the Sickle, as seen both in the individual profiles (Figures 6 a-h) and in Figure 8 (Plate 2), which shows the distribution of V$_{LSR}$ based on the Gaussian fits to the H92\a~line. The gradient in the southern extension of the Sickle is counter to galactic rotation, i.e. the velocities are lower at increasing longitudes. It is clear from Figure 8 (Plate 2) that the velocity is close to 0 \kms~ in region L3 at $\ell$=0\fdg19, b=-0\fdg045, which is in the center of the northern horizontal portion of the Sickle. There is a velocity gradient in both the NE and SW directions from this position with maximum values of \ab70 \kms~in the SW (region L8 at $\ell$=0\fdg155, b=-0\fdg044), and \ab75 \kms~at the NE edge (region L1 at $\ell$=0\fdg195, b=-0\fdg064). The velocity gradient is \ab25 ~\kms~arcminute${}^{-1}$~or \ab10~\kms~pc${}^{-1}$ over the N to SW portion of the Sickle, and about \ab60 \kms~arcminute${}^{-1}$ or \ab25~\kms~pc${}^{-1}$ over the N to NE portion of the Sickle. The range of values for V$_{LSR}$ (\ab5 to \ab 53 \kms) in the individual integrated profiles (Figures 6 a-h) is not as widespread because the extreme boxes (L1 and L8) do not completely extend to the ends of the Sickle. The large velocity gradient across the Sickle explains why the line width, $\Delta$$V_{FWHM}$, of \ab49 \kms~for the integrated profile shown in Figure 4a is much larger than the average value of \ab35 \kms~for the individual profiles (Figures 6 a-h). These line widths are in reasonable agreement with previously studied Galactic Center HII regions which have $\Delta$V$_{FWHM}$ \ab33 \kms~in Sgr B1 (Mehringer et al. 1992) and $\Delta$V$_{FWHM}$ \ab27 \kms~from a Galactic Center survey carried out by Downes et al. (1980). Figure 9a shows the distribution of the line widths in the Sickle based on the pixel by pixel fitting of the H92\a~line to the field. Two areas of extremely broad lines, i.e. $\Delta$V$_{FWHM}$ $>$ 50-60 \kms~are evident. These regions correspond to the places where a single component Gaussian is not an adequate fit to the more complex line profile. The expected line to continuum ratio in the H92\a~line for $\Delta$V$_{FWHM}$=35 \kms~and T$_{e}^{*}$\ab6000 K (typical LTE conditions) is $\sim$0.1. The distribution of H92\a~line amplitude based on the pixel by pixel fitting in this field is shown in Figure 9b. The integrated profile of the Sickle (Figure 4a) has a line to continuum ratio of 0.058\p.003. This depressed value is due to the extra continuum contribution from the NTF; of course there is no line emission from the NTF. The individual profiles (Figures 6 a-h) have line to continuum ratios in the range 0.06 to 0.17 (average value of \ab0.1). But, depending on the strength of the continuum from the NTF, the line to continuum ratio differs by varying amounts from the expected value of \ab0.1 in four of the regions where the NTF is present (L2, L3, L4, L6). Therefore the line to continuum ratio has been re-calculated using a comparison region of the NTF to correct for the increased continuum in both the individual profiles and the integrated profile. In regions L2 and L3, the line to continuum ratio is increased by 30\% after correction, and by 10\% in regions L4 and L6. The line to continuum ratio in the integrated profile (Figure 4a) was increased by \ab20\% after this correction. Electron temperatures,T$_e^*$, have been calculated for LTE conditions and an assumed Y$^{+}$=5\% (equation [22], Roelfsema \& Goss 1992). The T$_e^*$ for the individual regions of the Sickle, as listed in column 7 of Table 6, have not been corrected for the non-thermal contribution to the continuum emission. The corrected electron temperatures, T$_{e}^{*}$$_{C}$, in column 8, were calculated using the larger line to continuum ratios as discussed above. The average corrected electron temperature for the individual regions of the Sickle (Figures 6 a-h) is 4300\p750 K. The T$_{e}^{*}$ derived from the integrated H92\a~line profile of the Sickle (Figure 4a, Table 5) is 6500\p400 K. If we increase the line to continuum ratio of this profile by 20\%, an electron temperature of 5500\p400 K is derived. This value is in the range of average T$_e$ of Galactic center HII regions: 5000-7000 K (corrected for non-LTE effects) (Afflerbach et al. 1996). Similar values for T$_{e}^{*}$ have been observed in the Sgr B1 HII regions (T$_e^*$\ab 5050 K) (Mehringer et al. 1992). In the H110\a~recombination line Galactic center survey of Whiteoak \& Gardner (1973), the line to continuum ratio for the Sickle is extremely low (0.004) due to the sizable continuum contribution from the NTF with a 4\arcmin~beam. Similarly, the continuum contribution is significant in the value of T$_e^*$\ab 16,000 K which Downes et al. (1980) derive based on H110\a~line observations with a 2\farcm6 beam. Pauls et al. (1976) derive a value of T$_{e}^{*}$\ab 7000 K for an HII component near the Sickle from observations of the H85\a~recombination line; however, the velocity of their line is \ab -25 \kms, in contrast to the Sickle H92\a~linevelocity at +35 \kms. The values of T$^{*}_{e}$ of the Galactic Center Arc sources Pauls et al. (1980) observed with H109\a~are in the range 7800-12,000 K, with no correction for the NTF. Including the additional continuum, these electron temperatures would be reduced to a value of T$^{*}_{e}$ \ab5000 K, similar to the determination based on the current H92\a~data. The H92\a~line profiles for regions L9 and L10 are shown in Figures 6i and 6j. The source in L10, G0.21-0.00, has V$_{LSR}$ \ab 45 \kms, in agreement with previous studies which suggest that it is associated with the V$_{LSR}$ \ab50 \kms~Galactic center molecular cloud (Yusef-Zadeh 1986, Serabyn \& G\"{u}sten 1991). Region L9, a more diffuse component, shows line emission centered at V$_{LSR}$ \ab 5 \kms. \subsubsection{Recombination Lines in the Pistol} The mean V$_{LSR}$ for the H92\a~profile of the Pistol (Figure 4c) is \ab110 \kms, considerably higher than the mean V$_{LSR}$ of the Sickle (\ab35 \kms). There is a possible He 92\a~line in the Pistol with Y$^{+}$\ab14\p6\% (Figure 4c). In three regions (H2-H4; Figures 7 b-d) of the Pistol, the spatially integrated He 92\a~line is also detected with S/N of 2 to 4. The H92\a~velocity in regions H1-H4 (Figures 7 a-d) varies between 110 - 130 \kms. There is a double peaked profile in region H1 which has been fitted with components at V$_1$ \ab~130 \kms~and V$_2$ \ab~83 \kms~(separation \ab50 \kms). The velocity is \ab140 \kms~along the S central and E edge of the Pistol. The velocity decreases toward the N and W edges as seen in Figure 10a based on the pixel by pixel fit to the H92\a~line. The resulting velocity gradient is \ab1 \kms~arcsecond${}^{-1}$, or \ab 23 \kms~pc${}^{-1}$ across the Pistol. This gradient is somewhat lower than the value of \ab2 \kms~arcsecond${}^{-1}$ observed by Yusef-Zadeh, Morris, \& van Gorkom (1989). The line widths in the Pistol vary from 25-60 \kms. In the W portion of the Pistol (regions H3, H4), $\Delta$V$_{FWHM}$\ab40 \kms, which is wider than typical Galactic HII regions. However, in the E portion, the lines are more complex: very broad lines, $\Delta$V$_{FWHM}$\ab60 \kms, in region H2, and a double peaked line in region H1. This velocity structure combined with the observed velocity gradient results in a wide integrated profile ($\Delta$V$_{FWHM}$ \ab56 \kms) for the Pistol (Figure 4c). The poorer fit of a single Gaussian to the complex line profiles in the SE portion of the source explains the apparent broadening of the lines shown in Figure 10b. The line to continuum ratio for the Pistol is close to the expected value of \ab0.1. LTE electron temperatures have been calculated using Y$^+$=14\% for the integrated profile in Figure 4c, and for regions H1-H4 values for Y$^+$ as listed in Table 7. The T$_e^*$ based on the integrated Pistol profile (Figure 4c) is 3600\p300 K, somewhat lower than the T$_e^*$ of 5500 \p 400 K for the Sickle. \section {Discussion} \subsection{Velocity Field} \subsubsection{Velocity Gradient in the Sickle} One of the most striking aspects of the H92\a~recombination line observations of the Sickle is the prominent velocity gradient (Figure 8 (Plate 2)). From an area in the N central portion of the Sickle, the velocity increases rapidly in both the NE and SW directions. The change in direction of the velocity occurs at a position where the NTF appears to intersect the Sickle (in region L3, at $\ell$=0\fdg19, b=-0\fdg045). It is possible that the presence of the NTF in this region affects the ionized gas and perhaps causes the discontinuity in the velocity. Previous H110\a~recombination line observations (Yusef-Zadeh, Morris \& van Gorkom 1987) interpret the velocity pattern as gas flow along one of the NTF which intersects the Sickle in the N central region. Based on the coincidence in position and velocity of the CS J=3-2 molecular gas at 25 \kms~with the ionized gas, Serabyn \& G\"{u}sten (1991), Serabyn \& Morris (1994) suggest that the Sickle is the ionized edge of the V$_{LSR}$=25 \kms~cloud. However, the ionized gas shows a different velocity pattern than the molecular gas. At the N and S ends of the Sickle, the ionized gas has a much larger velocity, while the molecular gas shows only a modest change in velocity: \ab5 \kms~from the peak velocity of 25 \kms~across the cloud (Serabyn \& G\"{u}sten 1991). [O III] fine structure line observations (at 88$\micron$) show velocities in the Sickle of 20-90 \kms~increasing to the SW (Timmermann et al. 1996). The [O III] velocity only agrees with the H92\a~in the SW portion of the Sickle, where the H92\a~velocity is in the range 30-70 \kms~(see Figure 8 (Plate 2)). The [O III] line in the N and NW portions of the Sickle is very weak where the direction of increasing velocity changes. In the NE corner of the Sickle, the H92\a~velocity has a maximum of \ab70 \kms, while the [O III] velocity is only \ab20-30 \kms. \subsubsection{Double Profiles} Although the presence of double peaked profiles in HII regions often indicates an expanding shell of photoionized gas, this pattern does not appear to explain the velocity field in the Sickle. The regions of double profiles (L2, L3, L8; Figures 6b, 6c and 6h) are not observed in a single region or across the entire source. To the W and E of L2 and L3 the profiles are single (regions L1, L4; Figures 6a and 6d), and along the southern extension of the Sickle (Figures 6e, 6f, 6g), single components are also observed. A possible explanation of the double profiles is the presence of an additional HII component. In both the double peaked regions L2 and L3, there are negative velocity components. There is a large separation between the two components (\ab 100 \kms) in region L2; the positive component has a V$_{LSR}$=47.2\p1.5 and appears to be coincident with the velocity gradient to the W. Yusef-Zadeh (private communication) has pointed out that there is a weak H92\a~recombination line at \ab~-35 \kms, which has an \ab 1.5\arcmin~N to S extent from L2 towards the SW. The nature of this component is unclear, although it has been detected in the data observed by Yusef-Zadeh et al. (1989) and in the current observations. In L3, the positive (V$_{LSR}$=36 \kms) component also appears to be associated with the ionized gas which has a velocity decreasing to the W, whereas the negative (V$_{LSR}$=-17.3 \kms) component seems to be completely unrelated to the nearby positive velocities which characterize most of the ionized gas in the Sickle. It appears that the V$_{LSR}$=47 \kms~(L2) and V$_{LSR}$=36 \kms~(L3) components are associated with the ionized gas in the Sickle and are related to the V$_{LSR}$=25 \kms~molecular cloud; however, the origin of the negative velocity components is uncertain. In region L8, the V$_{LSR}$=53 \kms~component may be associated with the ionized gas in accordance with the velocity gradient, while the V$_{LSR}$=5 \kms~appears to be an unrelated component. It is possible that these additional, negative HII velocity components represent a feature which is interacting with the ionized edge of the molecular cloud, or perhaps are a detection of a part of this cloud which is located at the near side of the Sickle, in front of the NTF. In the previous VLA recombination line observations (Yusef-Zadeh et al. 1987, 1989) double peaked profiles have not been observed, but broad lines were detected in the Pistol (Yusef-Zadeh et al. 1989). Double peaks are also not seen in the [O III] 88$\micron$ line observations of the Sickle by Timmermann et al. (1996). However, the [O III] 88$\micron$ lines are significantly broader ($\Delta$V$_{FWHM}$ \ab110 \kms, compared to the typical \ab 70 \kms~line widths in their data) in regions of the Sickle where the double H92\a~lines are observed. In the Pistol a double profile is observed in region H1 (Figure 7a), and an unusually wide line (resolvable into two components) is observed in region H2 (Figure 7b). An expanding shell of photoionized gas is a possible explanation of the double profiles; however, if this were the case, double lines would be expected in the center of the Pistol, and narrower profiles at the edges. This pattern is not observed. The profiles are single and narrow across the entire W portion of the source (regions H3, H4) with a double profile located at the E edge (region H1). The increased width ($\Delta$V$_{FWHM}$ \ab 60 \kms) of the profile for region H2 (Figure 7b) is due to fitting a single component to a complex spectrum. Figure 11 shows a profile from a smaller area of this region (H2), in which a double peaked profile was fitted to the data. The components of this profile have velocities similar to those in the adjacent region H1, V$_1$\ab140 \kms, and V$_2$\ab85 \kms. It may be that the V$_{LSR}$\ab130 \kms~feature in regions H1 and H2 is associated with the main portion of the ionized gas centered at V$_{LSR}$\ab115 \kms; however the origin of the feature near \ab80 \kms~is uncertain. \subsection{H115\b~to H92\a~Ratio} The \b~to \a~line intensity ratio is a useful diagnostic of the physical conditions in HII regions. Under LTE conditions, the \b~to \a~ratio is expected to be 0.276. Traditionally, lower \b~to \a~ratios for radio recombination lines have been observed. These depressed ratios have been associated with pressure broadening at lower frequencies (Shaver \& Wilson 1979). The 8.31 GHz observations of the low density Sickle and Pistol HII regions are unlikely to be affected by such broadening. Thum et al. (1995) propose a model in which \b~to \a~ratios significantly higher than the LTE value are observed if the continuum optical depth, $\tau_{c}$, is much greater than 1. For optically thin sources ($\tau_{c}$ $<$ 1), with low density (n$_e$ $<$ 10$^6$ cm $^{-3}$), slight increases from the LTE \b~to \a~ratio are predicted. However, there is no available theory for enhanced \b~to \a~ratios in optically thin HII regions. The H115\b~to H92\a~ratio has been determined for the Sickle and Pistol in order to examine whether deviations of this ratio from the LTE value are correlated with the presence of the NTF. The \b~to \a~ratio for the integrated profile of the Sickle shown in Figure 4a (0.37\p.05) is consistent with the LTE value at the level of 2$\sigma$. The \b~to \a~ratio for the integrated Pistol profile in Figure 4b (0.38\p0.08) is also consistent with the LTE value. Most of the individual regions in the Sickle (7 of the 10 regions shown in Figure 6) have a \b~to \a~ratio (0.35\p0.07) consistent with LTE. However, three regions, located in the Sickle near L6, have \b~to \a~ratios in the range 0.40-0.56. Figures 12a and 12b show the distribution of the \b~to \a~ratio for the Sickle and Pistol. The H115\b~lines are very weak in the N central region of the Sickle (L2, L3); the upper limit for the \b~to \a~ratio is 0.2. Large \b~to \a~ratios ($>$ 0.5) are present in the SW portion of the Sickle (Figure 12a) as well as in the NW corner of the source, along the edges of the source. It is notable that at both of these positions, the NTF are present: however, there is no detailed correlation between the presence of the NTF and the \b~to \a~ratios. In the Pistol (Figure 12b) the \b~to \a~ratio is within the LTE range over most of the source. However, the S/N ratios in the detailed Pistol \b-line data (regions H1-H4) are too low to calculate the \b~to \a~line ratio. Figures 13 a-b show the H92\a~and H115\b~line profiles for a region in the SW Sickle ($\ell$=0\fdg17, b=-0\fdg040) where the ratio has a value of 0.59$\pm$0.06. The line shapes of the \a-line and \b-line profiles are quite similar. Although there is no current explanation for high ratios in optically thin HII regions, enhanced H98\b~to H76\a~ratios in the range of 0.30 to 0.40 have also been observed in the nearby Arched filaments (G0.1+0.08) (Anantharamaiah \& Yusef-Zadeh 1989). \subsection{Interaction with the Non-Thermal Filaments} At the positions of the double profiles in the Sickle (Regions L2, L3, and L8), the NTF appear to cross the HII region. The coincidence in position of the NTF and the ionized gas at these locations may provide insight into the origin of the double peaks. In looking for possible interactions of the NTF and the ionized and molecular gas, the relative positions of these sources should also be considered. Based on the alignment of the CS J=2-1 emission with a gap in the polarized synchrotron emission observed by Inoue et al. (1989), Serabyn \& G\"{u}sten (1991) conclude that the V$_{LSR}$=25 \kms~cloud is located in front of the NTF. Thus, the ionized edge of the molecular cloud would also be expected to lie in front of the NTF. The relative kinematics of the molecular cloud and the NTF are less certain. In their model for CIV ionization of the Sickle, Serabyn and G\"{u}sten (1991) proposed that the magnetic flux tube of the NTF is moving at a lower velocity (near V$_{LSR}$\ab0 \kms) than the ionized and molecular gas. However, strong 90 cm continuum absorption (Anantharamaiah et al. 1992) along the line of sight in the direction of the Sickle confirms that at least part of the Sickle is also located in front of the NTF. In each of the double profiles in regions L2, L3, and L8, one component has a V$_{LSR}$ which has a much lower velocity than the main portion of the ionized gas and appears unrelated as was discussed in 4.1.2. In each of these regions the NTF also intersects the Sickle. Therefore, it is possible that an additional component in the H92\a~line profile could be a detection of ionized gas related to the magnetic field associated with the NTF. In addition, the discontinuity in the velocity gradient (which may be related to the NTF) is exactly coincident with one of the double peaked regions, L3. The double peaks may be the result of an outflow of ionized gas from regions of intersection of the Sickle and NTF. The double profiles seem to indicate that the NTF is physically related to the ionized gas in several regions of the Sickle. The unusually wide [OIII] 88$\micron$ lines observed in the Sickle at positions where the H92\a~line is double (Timmermann et al. 1996) may be additional evidence for an association between the magnetic field and the HII region. Timmermann et al. (1996) interpret the broad lines as a superposition of the intrinsic line width and a component due to the velocity dispersion of the accelerated ions (O$^{++}$). These ions would have been accelerated at the surface layer of the HII region by the magnetic field. However, Timmermann et al. (1996) point out that the recombination line widths are not broadened significantly; they suggest that the recombination lines originate from the unaccelerated gas which is not in contact with the magnetic field. Based on the high resolution continuum image (Figure 3), it appears that the Pistol and the NTF are related, as Yusef-Zadeh \& Morris (1987b) indicate on morphological grounds. Based on the change in continuity and intensity of several of the NTF which pass through the source, Yusef-Zadeh \& Morris argue that an interaction between the Pistol and the NTF is likely. The current observations provide no new evidence for an interaction with the NTF. If the double peaked profiles are interpreted as a detection of the ionized gas interacting with the NTF, then such features would be expected along the N and S edges of the Pistol, where the NTF is present. However, the regions of complex line profiles are located throughout the central E portion of the Pistol and not correlated with the positions where the NTF intersect the source. \subsection{Source of Ionization} \subsubsection{Sickle} The recombination line properties of the Sickle are similar to other Galactic Center HII regions, such as the HII regions in the Sgr B2 star forming complex (Mehringer et al. 1992). In the Sickle, the T$_e^*$ and line widths (possible indicators of unusual excitation conditions) have values typical for Galactic Center HII regions and are fairly uniform across the source. Previous models for ionization of the Sickle relied on an association of the NTF with the gas in the regions of the Sickle where the NTF are present. Such models include the heating by relativistic particles related to the NTF (Yusef-Zadeh \& Morris 1987b) and the Critical Ionization Velocity (CIV) effect (Morris \& Yusef-Zadeh 1989; Serabyn \& G\"{u}sten 1991; Nicholls 1992). In both models, non-LTE conditions (differences in $T_e^*$, FWHM line widths, unusual \b~to \a~ratios) might be expected in regions where the NTF cross the source. The recombination line properties do not appear to change in the regions where the NTF are present; the line to continuum ratio, $\Delta$V$_{FWHM}$, and T$^*_e$ are essentially constant across the source. The only non-LTE conditions (enhanced \b~to \a~ratios) occur in one area of the Sickle (SW portion) and are not strongly correlated with the presence of the NTF (see Figure 12a). This result agrees with the CO J=6-5 and $^{13}$CO J=3-2 line observations (Harris et al. 1994), tracers of heating by relativistic particles, which show no enhancement in the regions where the NTF cross the Sickle. The CIV model (Serabyn \& Gusten 1991) predicts a shift between the molecular gas and the NTF of at least 25 \kms, in order that the neutral gas is ionized as it enters the region of magnetic field related to the NTF. In the regions of the Sickle with double peaked components (L2, L3, L8) (and where the NTF cross the source), a shift in the ionized components is observed. However this shift in velocity does not reveal that the CIV effect occurs between the molecular gas and the NTF. In addition, the FWHM line widths in these regions are not broadened as compared to typical values in Galactic Center HII regions (see sec 3.2.1). Unusually broadened might be an indication of an interaction which could cause ionization. Thus, the recombination line observations do not support the CIV mechanism. The observations of Harris et al. (1994) are also inconsistent with this mechanism; no velocity shift between an ion, HCO$^+$ and a neutral, HCN J=3-2, is observed. Although the source of ionization may not be the result of an interaction between the molecular cloud and the NTF, an association between the ionized gas and NTF might affect the velocity pattern observed in the Sickle as was discussed in section 4.3. UV photoionization is the most likely source of ionization of the Sickle. The line to continuum ratio, FWHM line widths, \b~to \a~ratio, and $T_e^*$ observed in the Sickle are in good agreeent with conditions in similar UV photoionized HII regions such as Sgr B1 and B2 (Mehringer et al. 1992, 1993). Based on the 8.3 GHz continuum, N$_{Lyc}$\ab2.8$\times$10$^{49}$ photons sec$^{-1}$ is derived for the Sickle. Recently, a group of He I and Br$\gamma$ emission line stars has been discovered in the infrared which are most likely members the Quintuplet cluster (Harris et al. 1994; Cotera et al. 1995; Figer et al. 1995, 1996). This cluster is assumed to be near the Galactic Center (Okuda et al. 1990) and located approximately at the center of curvature of the Sickle (see Figure 1). The inferred distance from the Quintpulet to the Sickle is at least 5 pc (Timmerman et al. 1996). Figer et al. (1995, 1996) have identified eight Wolf Rayet stars (four WN and four WC types), two WN9/Ofpe stars, fourteen OB supergiants, in addition to the LBV candidate; all of these stars contribute to the total ionizing flux, N$_{Lyc}$ \ab 8$\times$ 10$^{49}$ photons sec$^{-1}$. Of course, geometric dilution will reduce the Lyman continuum radiation field at the position of the Sickle. Based on integration of the 32 GHz radio continuum flux density distribution over a 2\farcm5 area near the Quintuplet Cluster (Lesch \& Reich 1992), Timmermann et al. (1996) estimate that the Sickle is excited by the equivalent of 50-100 O8 stars or 0.3-14 O6 stars. From the detection of these massive hot stars (Figer et al. 1995, 1996), Timmerman et al. (1996) infer that massive star formation has recently occured ($<$ 10$^7$ years ago) in the Galactic Center and that a sufficient number of O and B stars may be available to ionize the gas in the Sickle. \subsubsection{Pistol} The recombination line properties of the Pistol (line to continuum ratio, \b~to \a~ratio) are also consistent with ionization by hot stars. However, the low T$_e^*$ (\ab3600 K) and complex velocity structure in the SE portion of the Pistol are unusual. Mehringer et al. (1993) suggest that differences in T$_e^*$ between Sgr B1 (T$_e^*$\ab5050 K) and Sgr B2 (T$_e^*$\ab7150 K) could be due to a difference in metallicity in these two prominent Galactic Center HII regions. The Pistol (T$_e^*$\ab3600 K) and the Sickle (T$_e^*$\ab5500 K) may also reflect such differences. Although a number of possible ionizing sources for the Pistol have been detected in the Quintuplet cluster, both Cotera et al. (1995) and Figer et al. (1995) suggest that the star located at the center of curvature of the Pistol may be responsible for its ionization. Figer et al. (1995) have proposed that this star is an LBV (Luminous Blue Variable) with the flux of a B0I star and T$_{eff}$\ab30,000 K; N$_{Lyc}$\ab3.4$\times$10$^{48}$ photons sec$^{-1}$ would be produced. Based on the 8.3 GHz continuum, the Pistol requires N$_{Lyc}$\ab5$\times$10$^{48}$ photons sec$^{-1}$. Considering geometric dilution, additional stars may be needed to fully ionize the Pistol. Figer et al. (1996) suggest that the newly identified WC8 star, located near the LBV candidate at RA: 17\fh43\fm4\fs4, DEC: -28\arcdeg48\arcmin53\farcs8, may contribute to the ionization of the Pistol. This star has a larger continuum flux than the LBV candidate, N$_{Lyc}$\ab5 $\times$10$^{48}$ photons sec$^{-1}$. Figer et al. (1995) further suggest that the Pistol is a nebula created by an earlier evolutionary stage of the LBV candidate. Recombination line features similar to those observed in the Pistol (low T$^*_e$, complex velocity structure) have been observed near G25.5+0.2 (Shepherd et al. 1995), an object thought to be a nebula ejected from a star during the LBV phase. No molecular gas is associated with G25.5+0.2, indicating that it is an evolved object. The low temperature in G25.5+0.2 (\ab6200 K) is attributed to the enhanced metallicity of the enriched nebula. The double lines (region H1, Figure 7a) and complex lines (wide lines resolved into a double profiles in region H2, shown in Figure 11) are located in portions of the Pistol centered on the LBV candidate. Based on the lack of molecular gas associated with the Pistol (Serabyn \& G\"{u}sten 1991) and the low T$_e^{*}$ compared to the nearby Sickle, it is possible that the Pistol is material ejected from the LBV candidate. At the position of the LBV candidate, the velocity structure differs from the remainder of the source; complex wide lines and double component profiles suggest expansion of the ionized gas outwards from the central SE portion of the Pistol. An association between the gas in this region and the LBV candidate is therefore possible. \section{Helium Abundance} A probable He 92\a~recombination line has been detected in the Pistol with S/N in the range 2-4; however, no lines were detected in the Sickle. The Y$^+$ values in these sources differ by at least a factor of three (Pistol Y$^+$=14\p6$\%$, Sickle Y$^+<$5\%). The difference in helium abundance could indicate a difference in metallicity; however, the more likely explanation is that the radiation field of the Pistol may be significantly harder than that of the Sickle. The hot stars in the vicinity of the Pistol ($T_e$ $>$ 35,000 K) will produce harder photons with h$\nu$ $>$ 24.6 eV and the Str\"{o}mgren sphere of helium and hydrogen would then coexist. However, Timmermann et al. (1996) appear to observe the opposite effect. They suggest that the lack of a detectable [O III] line in the Pistol may be due to either a beam dilution effect (beam \ab22\arcsec), or a softer radiation field ($<$ 35,000 K) compared to the Sickle. \section{Conclusions} Using the VLA, the 8.3 GHz continuum and H92\a~and H115\b~recombination lines have been observed in the Sickle and Pistol HII regions near $\ell$=0\fdg18, b=-0\fdg04. These observations were made to investigate the possible interaction between the thermal sources and the non-thermal filaments (NTF). (1) In addition to the H92\a~and H115\b~lines, a probable He 92\a~line is detected in the Pistol with an average Y$^{+}$\ab14\p6\%. In the Sickle, He 92\a~is not detected with an upper limit for Y$^+$$<$ 5\% at a 3$\sigma$ level. (2) The H92\a~mean V$_{LSR}$ in the Sickle is \ab 35 \kms~with additional negative velocity components detected in two regions of the N central Sickle. A pronounced velocity gradient is observed with positive velocities increasing from \ab0 \kms~to \ab75 \kms~to the W and S of $\ell$=0\fdg19, b=0\fdg040 in the Sickle. Double profiles in three regions of the Sickle (where the NTF intersect the HII region) provide evidence for an interaction between the NTF and ionized gas. (3) The H92\a~mean V$_{LSR}$ in the Pistol is \ab 115 \kms, \ab80 \kms~higher than the Sickle. A velocity gradient of 1 \kms~arcsecond$^{-1}$ is observed across the Pistol. The pattern of line profiles is complex: in the SE portion of the source, the profiles are broad or double; in the W part, the profiles are single and narrow. (4) The recombination line properties of the Sickle and Pistol (line to continuum ratio, $\Delta$V$_{FWHM}$, T$_{e}^{*}$, \b~to \a~ratios) are similar to typical photoionized HII regions. The line properties are roughly constant across the sources, and the slight deviations are not correlated with positions where the NTF cross the HII regions. The \b~to \a~ratio is enhanced in the SW portion of the Sickle. Such a strong enhancement in the \b-line has not previously been observed in HII regions. The T$^*_e$ in the Pistol is \ab 2000 K lower than in the Sickle, indicating a possible difference in the radiation field of the Sickle and Pistol. (5) The unusual recombination line properties of the Pistol (low T$_e^*$ and complex line structure in the SW portion of the source) are similar to those observed in G25.5+0.2, a nebula associated with an LBV star. Therefore, it is possible that the LBV candidate located at the center of curvature of the Pistol is responsible for the ionization of the source, as suggested by Figer et al. (1995). The population of He I and Br$\gamma$ emission line stars which has been detected near the Quintuplet Cluster, are the most likely ionizing sources of the Sickle. \acknowledgments{The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under a cooperative agreement by Associated Universities, Inc. The authors thank Paula Benaglia for assistance in the early stages of this work (1992-3). Lang would like to acknowledge the REU (Research Experience for Undergraduates Program) of the National Science Foundation administered by NRAO in Socorro, NM, during the summer of 1994. We would also like to thank Chris DePree, Alison Peck, Don Figer, Mark Morris, Lanie Dickel, Pat Palmer, Dave Mehringer, Mark Claussen, Dave Adler, and Angela Cotera for their useful comments and suggestions during the later stages of this research.} \clearpage \begin{table} \caption{Parameters of the H92\a~and H115\b~Observations} \begin{center} \begin{tabular}{cccc}\hline\hline \def\baselinewidth{.96} Array &DnC(H92\a) &CnB(H92\a) &DnC(H115\b)\\ Dates &25 June 92 &24 May 93 &25, 27 Sept 93\\ Total Obs. Time &8 h &8 h &8.5 h\\ \hline \end{tabular} \begin{tabular}{lc} \def\baselinewidth{.96} R.A. of Field Center (B1950) &17\fh43\fm04\fs0\\ Dec. of Field Center (B1950) &-28\arcdeg47\arcmin30\arcsec\\ LSR Central Velocity &50 \kms \\ Total Bandwidth &12.5 MHz (45 \kms)\tablenotemark{*}\\ Number of Channels &64\\ Channel Separation &195.3 kHz (7.0 \kms)\tablenotemark{*}\\ Velocity Resolution &234.4 kHz (8.5 \kms)\tablenotemark{*}\\ Rest Frequencies \\ \it H92\a &8309.383 MHz\\ \it H115\b &8427.314 MHz\\ Flux Density Calibrator &3C286\\ Phase Calibrator &NRAO 530 (1730-130)\\ \hline\hline \end{tabular} \tablenotetext{*}{For H92\a} \end{center} \end{table} \begin{table} \caption{Parameters of the H92\a~and H115\b~Images} \begin{center} \begin{tabular}{lccc}\hline\hline Image & H92\a\tablenotemark{\dag}&H92\a\tablenotemark{\ddag} &H115\b\tablenotemark{\ddag}\\ \hline\hline \def\baselinewidth{.96} FWHM of synthesized beam \it (arcsec) &6.69 x 4.70 &12.30 x 6.29 &12.30 x 6.28\\ Position Angle &3\arcdeg &-35\arcdeg &-35\arcdeg\\ RMS noise {\it (mJy/beam)}\\ continuum &1.1 &3.2 &3.6\\ line &0.28 &0.27 &0.34\\ \hline\hline \end{tabular} \tablenotetext{\dag}{``high'' resolution data} \tablenotetext{\ddag}{``low'' resolution data} \end{center} \end{table} \begin{table} \caption{Parameters of the Sources near the Sickle and Pistol} \begin{center} \begin{tabular}{lcccc} \hline\hline Source &Right Ascension & Declination &Total Flux & Deconvolved\\ & (B1950) & (B1950) & Density& Size \\ \hline\hline \def\baselinewidth{.96} N1 (G0.10-0.05) &17\fh42\fm52\fs45\p.01 & -28\arcdeg51\arcmin37\farcs0\p0.1 & 47\p5 mJy &1.9\arcsec\\ N3 (G0.17-0.08) &17\fh43\fm10\fs57\p.01 & -28\arcdeg48\arcmin56\farcs5\p0.1 &20\p3 mJy & 1.1\arcsec\\ O1 (G0.21-0.00)\tablenotemark{*} & 17\fh42\fm56\fs96\p.01 & -28\arcdeg44\arcmin26\farcs4\p0.1 & 150\p20 mJy& 7.0\arcsec\\ \hline\hline \end{tabular} \tablenotetext{*}{The 2.8\arcsec~core has a flux density of \ab70~mJy.} \end{center} \end{table} \clearpage \begin{table} \begin{center} \caption{Properties Derived from the Radio Continuum} \begin{tabular}{lcccccccc}\hline\hline Source& S$_{\nu}$&Size & Radius & n$_e$ & EM&M$_{HII}$ & N$_{Lyc}$ & $\tau_{c}$\\ &(Jy)&(\arcsec)&(pc)&(cm$^{-3}$)&(pc cm$^{-6}$) &(M$_{\sun})$&(s$^{-1})$& (8.3 GHz)\\ \hline\hline \def\baselinewidth{.96} Sickle & 3.0 &30$\times$180 & 2.2 & 220 & 2.1$\times$10$^{5}$& 240 & 2.8$\times$10$^{49}$ & 0.002\\ Pistol & 0.5 &12$\times$30 & 0.6 & 640 &4.7$\times$10$^{5}$ &11 &5.6$\times$10$^{48}$ &0.007\\ O1 &0.15 &7 & 0.2 & 1700 & 1.2$\times$10$^{6}$ & 1.6 & 1.4$\times$10$^{48}$ & 0.01\\ \hline\hline \end{tabular} \end{center} \end{table} \begin{table} \caption{Gaussian Fits to the Integrated Profiles over the Sickle and the Pistol shown in Figure 4 a-d} \begin{center} \begin{tabular}{lccccc}\hline\hline Region & line & T$_{l}$/T$_{c}$ & V$_{LSR}$ &$\Delta$V & T$_{e}^*$ \\ & & &(\kms)& (\kms)& (K)\\ \hline\hline \def\baselinewidth{.96} Sickle & \it H92\a &0.058\p.003 &34.0\p0.8 &48.7\p2.1 &6500\p400 ($T^{*}_e$$_{C}$ \ab 5500\p400 K)\tablenotemark{\dag}\\ & \it H115\b &0.022\p.002 &34.8\p1.3 &48.6\p3.3 \\ Pistol & \it H92\a &0.092\p.006 &111.0\p1.1 &55.9\p2.7 &3600\p300\\ & \it He 92\a &0.013\p.006 &100.2\p6.4 &56.9\p17.0\\ & \it H115\b &0.040\p.006 &121.0\p1.6 &48.1\p4.7 \\ \hline\hline \end{tabular} \tablenotetext{\dag}{Electron temperature corrected for additional continuum} \end{center} \end{table} \clearpage \begin{table} \caption{Gaussian Fits to the Integrated Line Profiles in the Sickle shown in Figures 6 a-j} \begin{center} \begin{tabular}{lccccccc}\hline\hline \def\baselinewidth{.96} Region & Figure &T$_{l}$/T$_{c}$ & V$_{LSR}$ & $\Delta$V & \b/\a~ &T$_{e}^*$ & T$_{e}^*$$_{C}$\tablenotemark{\ddag} \\ No. & No. & & (\kms) & (\kms) & & (K) & (K) \\ \hline\hline \def\baselinewidth{.96} L1 &6a &0.11\p.01 & 52.3\p1.4 &47.9\p3.8 &0.27\p.05 &3800\p400& ... \\ L2 &6b &0.064\p.009 &47.2\p1.5 &34.7\p3.6 & 0.31\p.07 &8100\p1200 &5300\p1500\\ & ... &0.023\p.007 &-49.8\p3.2 &35.9\p8.0 & 0.30\p.10& ... & ...\\ L3 &6c &0.048\p.007 &35.7\p1.8 &42.9\p4.3 &0.32\p.07 &7400\p1500 &5400\p900\\ & ... &0.038\p.007 &-17.3\p2.1 &37.8\p4.9 &0.33\p.10 & ... &...\\ L4 &6d &0.099\p.009 &8.0\p0.9 &35.0\p2.3 &0.47\p.06 &5400\p600 &3200\p300\\ L5 &6e &0.106\p.008 &23.1\p0.8 &38.4\p2.0 &0.44\p.05 &5000\p400 & ... \\ L6 &6f &0.113\p.007 &31.2\p0.7 &33.7\p1.6 &0.56\p.07 &5000\p300 &3500\p300\\ L7 &6g &0.20\p.01 &41.7\p0.6 &28.2\p1.4 &0.47\p.05 &3500\p200 &...\\ L8 &6h &0.17\p.01 &53.0\p0.7 &29.8\p1.8 &0.34\p.04 &3100\p300 & ...\\ & ... &0.13\p.02 &5.9\p0.08 &21.7\p2.0 &0.15\p.05 & ...& ...\\ L9 &6i &0.111\p.009 &4.87\p1.0 &38.8\p2.5 &0.22\p.04 &4500\p400& ... \\ L10\tablenotemark{\dag} &6j &0.13\p.02 &45.2\p1.1 &26.2\p2.7 &0.17\p.05 &5500\p400& ... \\ \hline\hline \end{tabular} \tablenotetext{\dag}{O1 (G0.21-0.00)} \tablenotetext{\ddag}{Electron temperatures corrected for additional continuum} \end{center} \end{table} \clearpage \begin{table} \caption{Gaussian Fits to the Integrated Line Profiles in the Pistol shown in Figures 7 a-d} \begin{center} \begin{tabular}{lccccccc}\hline\hline \def\baselinewidth{0.96} Region & Figure & T$_{l}$/T$_{c}$ & V$_{LSR}$ & $\Delta$V$_{FWHM}$ & T$_e^*$ & He92$\alpha$~V$_{LSR}$ & Y$^+$ \\ No. & No. & & (\kms) & (\kms) & (K) & (\kms) & (\%) \\ \hline\hline H1 &7a &0.103\p.015 &130.3\p1.0 &25.3\p2.4 &5200\p800 &... & ... \\ &... &0.055\p.011 &83.3\p2.8 &47.8\p7.4 &... & ... & ... \\ H2 &7b &0.086\p.005 &108.9\p0.9 &60.3\p2.2 &3700\p300 &100.8\p5.2 & 8\p5\\ H3 &7c &0.107\p.006 &106.8\p0.7 &40.6\p1.7 &4200\p300 &99.7\p4.5 & 11\p6\\ H4 &7d &0.117\p.008 &110.0\p0.9 &48.2\p2.3 &3200\p300 &99.7\p2.8 &19\p7\\ \hline \hline \end{tabular} \end{center} \end{table} \clearpage \begin{references} \reference{A1} Afflerbach, A., Churchwell, E., Acord, J.M, Hofner, P., Kurtz, S, and DePree, C.G. 1996, \apjl, in press \reference{A3} Anantharamaiah, K.R. and Yusef-Zadeh, F. 1989, The Center of the Galaxy, M. 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Tabara, H., and Kato, T. 1989, The Center of the Galaxy, M. Morris, ed., Kluwer: Boston, IAU Symp. 136, 269 \reference{L} Lesch, H. and Reich, W. 1992, \astap, 264, 493 \reference{L2} Liszt, H.S., and Spiker, R.W. 1995, \apjs, 98, 259 \reference{M1} Mehringer, D.M., Yusef-Zadeh, F., Palmer, P., and Goss, W.M. 1992, \apj, 401, 168 \reference{M2} Mehringer, D.M., Palmer, P., Goss, W.M., and Yusef-Zadeh, F. 1993, \apj, 412, 684 \reference{M3} Mezger, P.G. and Henderson, A.P. 1967, \apj, 147, 471. \reference{M5} Moneti, A., Glass, I.S., and Moorwood, A.F.M. 1991, Mem. Soc. Astr. 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Barnes, eds., Astronomical Society of the Pacific Conference Series: San Fransisco, 131 \reference{W} Whiteoak, J.B. and Gardner, F.F. 1973, Astrophysical Letters, 13, 205 \reference{YZ1} Yusef-Zadeh, F. 1986 Ph.D. thesis, Columbia University \reference{YZ2} Yusef-Zadeh, F., and Morris, M. 1987a, \apj, 322, 721 \reference{YZ3} Yusef-Zadeh, F., and Morris, M. 1987b, \aj, 94, 1178 \reference{YZ4} Yusef-Zadeh, F., Morris, M., and Chance, D. 1984, Nature, 310, 557 \reference{YZ5} Yusef-Zadeh, F., Morris, M., and van Gorkom, J.H. 1987, The Galactic Center, Backer, D.C., ed., AIP: New York, 190 \reference{YZ6} Yusef-Zadeh, F., Morris, M., and van Gorkom, J.H. 1989, The Center of the Galaxy, M. Morris, ed., Kluwer: Boston, IAU Symp. 136, 275 \reference{YZ7} Yusef-Zadeh, F., private communication, Februrary 1996 \end{references} \clearpage \figcaption[f1.eps]{Schematic representation of the sources discussed in this paper: the Sickle and Pistol HII regions and various point sources, the linear non-thermal filaments (NTF), the Quintuplet Cluster and the LBV candidate star. Lines of constant Galactic latitude and longitude are indicated.} \figcaption{Uniformly weighted 8.3 GHz continuum image of the Sickle and the Pistol with a resolution of 2\farcs04~x 1\farcs71, PA=59\arcdeg. This pseudo-color image is not corrected for primary beam attenuation. The peak intensity is 10.5 mJy/beam. The rms noise is 0.2 mJy/beam.} \figcaption[f3.eps]{8.3 GHz continuum image centered on the Sickle and Pistol HII regions, with the ``high'' resolution of 6\farcs69 x 4\farcs70, PA=3\arcdeg. Contours are at -5, 1, 5, 10, 15, 20, 25, 30, 35, 40 mJy/beam levels.} \figcaption[f4ab.ps, f4cd.ps]{The spatially integrated, continuum weighted profiles for the Sickle and Pistol. The line to continuum ratio (values represented by vertical bars) is plotted against LSR velocity. Data points, model curve, and residuals are shown for the Sickle: (a) H92\a~and (b) H115\b~lines, and for the Pistol: (c) H92\a~and He 92\a~and (d) H115\b~lines.} \figcaption[f5a.ps, f5b.ps]{(a) 8.3 GHz continuum image of the Sickle and Pistol with the the ``low'' resolution of 12\farcs30 x 6\farcs29, PA=-35\arcdeg. Contours are at -5, 5, 15, 25, 35, 45, 55, 60 mJy/beam levels. (b) 8.3 GHz ``high'' resolution continuum image (see Figure 3) of the Pistol. Contours are at -5, 1, 5, 10, 15, 20, 25, 30, 35, 40 mJy/beam levels. The boxes represent regions over which the recombination lines were spatially integrated to obtain the line profiles shown in Figures 6 a-j and 7 a-d.} \figcaption[f6ad.ps, f6eh.ps, f6ij.ps]{The spatially integrated, continuum weighted H92\a~line profiles for the 10 regions of the Sickle and nearby sources represented in Figure 5a (from the ``low'' resolution data). The format is identical to Figure 4. For seven of the regions, the line profiles were fitted with a single Gaussian component. Regions L3 (Figure 6c) and L8 (Figure 6h) the lines were fitted with two Gaussian components. Region L2 was also fitted with two Gaussian components (see Table 7), while Figure 6b shows a fit only to the major component at $V_{LSR}$\ab47 \kms.} \figcaption[f7ad.ps]{The spatially integrated, continuum weighted H92\a~line profiles for the 4 regions of the Pistol represented in Figure 5b (from the ``high'' resolution data). The format is identical to that Figure 4. In addition to the H92\a~component, the line data for three regions were also fitted with a probable He 92\a~component, while for region H1 (Figure 7a) the H92\a~line was fitted with two Gaussian components.} \figcaption{Distribution of velocity in the Sickle and Pistol, based on fits to the ``high'' resolution H92\a~line data, overlaid on the corresponding 8.3 GHz continuum image. LSR velocities (\kms) are shown as the false color scale and the continuum is shown as contours at -5, 5, 10, 15, 30, 45 mJy/beam levels.} \figcaption[f9a.ps, f9b.ps]{Parameters from the Gaussian fits to the ``high'' resolution H92\a~line in the Sickle and Pistol, overlaid on the 8.3 GHz continuum image. Shown as greyscale: (a) FWHM line width (\kms) and (b) the line amplitude (mJy/beam). Continuum contours are at -5, 1, 5, 15, 30, 45 mJy/beam levels.} \figcaption[f10a.ps, f10b.ps]{Parameters from the Gaussian fits to the Pistol based on the ``high'' resolution data, overlaid on the 8.3 GHz continuum image. Continuum shown by contours at -5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 mJy/beam. Shown in greyscale are the (a) velocity (\kms) and (b) FWHM line width (\kms).} \figcaption[f11.ps]{Double component profile in the Pistol at $\ell$=0\fdg155, b=-0\fdg065, based on the ``high'' resolution data which was fitted with components at V$_1$\ab140 \kms~and V$_2$\ab86 \kms.} \figcaption[f12a.ps, f12b.ps]{Distribution of the H115\b~to H92\a~line ratio based on the the ``low'' resolution data, overlaid on the corresponding 8.3 GHz continuum image. The continuum are contours at -5, 1, 5, 15, 30, 45 mJy/beam. The ratio is shown as greyscale for the (a) Sickle and (b) Pistol.} \figcaption[f13.ps]{Spatially integrated, continuum weighted H92\a~and H115\b~line profiles for a region in the SW Sickle (at $\ell$=0\fdg17, b=-0\fdg040) which has an enhanced \b~to \a~ratio of 0.59\p.06.} \end{document} t ----- End Included Message -----