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\begin{document}

\title{Hot Stars in the Quintuplet}

\author{Donald F. Figer, Mark Morris, and Ian S. McLean}
\affil{Division of Astronomy, Department of Physics \& Astronomy, 
University of California, Los Angeles, CA  90095}

\begin{abstract}

     We present K-band spectra of newly identified hot stars in the
Quintuplet cluster, as well as template spectra for 34 Galactic
Wolf-Rayet stars. Five of the new stars are WR types (3 WC and 2 WN),
while 14 others are OB supergiants; three of the WR stars are probably
the hottest identified stars within 50 pc of the Galactic Center. The
newly identified stars increase the estimated ionizing flux from this
cluster by about an order of magnitude with
respect to earlier estimates, to $8.2(10^{49})$ photons s$^{-1}$, or about  
one third of
what is required to ionize the ``Sickle'' (G0.18-0.04). In addition, we 
propose that the 5 original enigmatic members of the
Quintuplet-proper are dusty WCL stars, similar to the dozen or so known
examples in the Galaxy.

\end{abstract}

\section{Introduction}

     The Quintuplet is a cluster of young stars located approximately
35 pc, in projection, from the Galactic Center. In addition to the 5
bright stars for which the Quintuplet was named (Nagata et al.\ 1990;
Okuda et al.\ 1990), there is a clustering of many more stars in the
vicinity. Our image clearly shows a diffuse background of light
from unresolved stars which spans a diameter of $\approx$ 50$\arcsec$. Beyond
this, cluster members are indistinguishable, in continuum images, 
from the already crowded field of stars in this part of the sky.

     While the nature of the 5 Quintuplet members has been unclear,
several of the cluster stars are now known to be evolved massive stars
only a few million years old (Figer, McLean \& Morris 1995; hereafter FMM95; Moneti,
Glass \& Moorwood 1994; Harris et al.\ 1994; Cotera et al.\ 1996). 
This
cluster is proving to be key to understanding many important questions, i.e. 1)
Is the cluster in the inner parsec of the Galaxy really ``unique'', i.e., are 
extraordinary physical processes required to explain the exsistence of the
central cluster? 2) Do hot stars in the Quintuplet ionize G0.18-0.04 
(the ``Sickle'') and G0.15-0.05 (the ``Pistol'')? 3) Does the initial mass 
function (IMF) in the 
Galactic Center favor high-mass stars? 4) Is the Quintuplet population consistent
with stellar evolution models which predict that WR/(WR+O) and WC/(WR+O) should be elevated
in higher metallicity regions?
 

\section{Observations and Data Reduction}

     All data were taken with the UCLA double-beam near-infrared
camera (McLean et al.\ 1993; McLean et al.\ 1994) at the University of
California Observatories' 3-m Shane telescope. H and K grisms were used to 
produce spectra with R $\approx$ 525 (Figer 1995).
The data were reduced according to the procedure in Figer (1995). 
Table 1 gives the identifications, coordinates, photometry,
spectral classifications, and estimated ionizing fluxes for the target
stars. Reference codes are shown at the bottom of the table. K-band
magnitudes were converted from K$^{\prime}$ using the relation in Wainscoat \&
Cowie (1992).

\section{K-band Spectra}

     K-band spectra for Galactic WR stars are shown in Figure 1. The emission lines
tend to follow the expected trend of greater equivalent width for higher
ionization species with earlier subtype. K-band classification is more
effective in distinguishing different subtypes amongst the WN sequence
than the WC sequence. Both WN9 stars lack HeII emission at 2.189 $\mu$m
while WN8 stars show a hint of it. This is the strongest feature in earlier
WN stars. The WC stars tend to all have similar spectra except for the
latest types (WC8 and WC9). WR112 and WR118 have featureless spectra,
presumably due to dilution by dust emission (Williams, van der Hucht 
\& The 1987). Spectra for the target stars are shown in Figure 2. 
They have been dereddened as in FMM95.

\section{Spectral Classifications}

     The WR stars were classified by comparing their spectra to the
spectra in Figure 1 and by comparing their flux excesses at 3.09 $\mu$m to
those measured in Galactic WR stars (Figer 1995). The new WN9 stars, qF256
and qF274, have line widths similar to qF320 (FMM95-1), and they lack 
HeII emission (2.189 $\mu$m). The new WN6 star, qF353e, has prominent
emission at 2.189 $\mu$m which is comparable to the emission line strength
near 2.166 $\mu$m; it also has a considerable excess at 3.09 $\mu$m. The new WC
stars all have similar spectra, lacking the prominent emission at 2.058
$\mu$m which is usually seen in WC9 stars (FMM95).  Two of the stars, qF309
and qF235, are classified as earlier than WC8 for their excesses at 3.09
$\mu$m, while qF151 has very little excess there. Together, the
WN6 and the two ``$<$WC8'' stars are probably the hottest identified
stars within 50 pc of the Galactic Center, although their ionizing
fluxes are quite meager owing to their small radii (Schmutz 1996).

     The ``OBI'' stars were classified using the new atlases from Hanson \&
Conti (1996) and Tamblyn et al.\ (1996). The ``$<$B0I'' stars have a 
featureless continuum.
Their K-band magnitudes put them in the supergiant class, and their
featureless spectra can only be fit by stars earlier than B0I. The ``OBI'' stars
have Br$\gamma$ and HeI (2.058 $\mu$m) in
emission with HeI (2.112/2.113 $\mu$m) in absorption. The spectra are
similar to those of HD207329 (B1.5IB:e; Tamblyn et al.\ 1996) and BD+36 4063
(ON9.7Ia; Tamblyn et al.\ 1996 and Hanson \& Conti 1996). It should
be noted, though, that ON9.7Iab stars in Hanson \& Conti (1996) have
all three diagnostic features in absorption. The early BI stars were classified by
measuring the equivalent widths in these three spectral lines and
comparing these values to those in the atlases.

\section{Mass and Age of the Quintuplet}

     We can estimate the total cluster mass by integrating the IMF
from the upper mass cutoff down to the lowest mass star identified in
Table 1. Assuming, conservatively, that 32 stars in the table have masses between
m$_{u}$ = 100 M$_{\sun}$ and m$_{o}$ = 20 M$_{\sun}$, we calculate M$_{cluster}$
$\approx$ 5500 M$_{\sun}$ (3700 M$_{\sun}$) for m$_{l}$ = 0.1 M$_{\sun}$ 
(1 M$_{\sun}$) and an IMF slope of $-2$.
We can make an independent estimate by assuming that the cluster
is bound against tidal disruption, the orbital velocity is equal
to the line-of-sight velocity (130 km s$^{-1}$; Figer 1995), and the projected 
distance from the GC (35 pc) is equal to the orbital radius.
For these parameters, the orbital time
for the cluster is $\approx$ 1.7(10$^{6}$) yrs assuming a circular orbit. The enclosed
mass at this radius is $\approx$ 2(10$^{8}$) M$_{\sun}$ (McGinn et al.\ 1989). 
Using the tidal equation, we find M$_{total}$ = (2M$_{r<35 pc}$) $\times$ 
(r$_{Quin}$/35 pc)$^{3}$ = 9,300 M$_{\sun}$, where r$_{Quin} $
is the average distance of the stars in the table from the center of the cluster
and is $\approx$ 1 pc.
If O-stars are still present, then the cluster age is between 2.5 to 4.7(10$^{6}$) 
yrs depending on the mass-loss rates and the metallicity, assuming an IMF slope of $-2$ (Meynet
1995). Otherwise, the age may be up to 8(10$^{6}$) yrs.

\section{Ionizing Flux}

     Harris et al.\ (1994) estimate that the Sickle requires a Lyman
continuum flux of Q$_{o} \approx$ 3(10$^{50}$) s$^{-1}$, and, according to 
Yusef-Zadeh, Morris \& van Gorkom (1989), the Pistol requires 
Q$_{o} \approx$ 3.9(10$^{48}$) s$^{-1}$. Timmermann et al.\ (1996) use 
the radio flux at 32 GHz to estimate that the Quintuplet produces 
Q$_{o} \approx$ 1.6(10$^{50})/\eta$ s$^{-1}$, where $\eta$ is less than 1 and 
accounts for dust absorption and deviations from an ionization-bounded region. 
We have estimated contributions to Q$_{o}$ from each classified star in the
Quintuplet. The results are given in Table 1 and the total is 
Q$_{o,tot} \approx$ 8.2(10$^{49}$) s$^{-1}$. The OB stars presented here 
represent some of the previsouly predicted population (Harris 
et al.\ 1994; FMM95; Timmermann et al.\ 1996), and it is still possible that 
main sequence O-stars might be contributing to Q$_{o}$. FMM95 estimate an ionizing 
flux of 3.4(10$^{48}$) s$^{-1}$ from FMM95-3
(the LBVc). This is adequate to ionize the Pistol, although
contributions from other hot stars in the Quintuplet may be
important, i.e. qF151 (WC8).

\section{The Quintuplet-proper Members}

     The Quintuplet-proper members (QPMs) have remained a mystery
since their discovery. Some have suggested that they are protostars, or at least
not giants or supergiants (Okuda et al.\ 1990; Nagata et al.\ 1990; Glass, 
Moneti \& Moorwood 1990). We now suggest that these objects are 
dusty WCLs (c.f. Abbott \& Conti 1987; Williams, van der Hucht \& 
The 1987; Cohen 1995). DWCL stars represent relatively short-lived phases 
of evolution when the coolest WC types (WC8 and WC9) tend to form 
dust shells. Williams, van der Hucht \& The (1987) find that 19/27 of the 
WC8 and WC9 they studied have circumstellar dust emission. The near-infrared 
emission from these shells is well-fit by a black-body of 780-1650 K. 
Spectra for WR112 and WR118 are representative of the class.

     We have calculated apparent K-band magnitudes that various Galactic WC9 stars 
would have if they were in the Quintuplet. The most striking result is 
that m$_{K}$ spans a very large range, $\approx$ 3 (WR112) to 12 (WR92). This
is, presumably, due to the different amounts of dust emission from each
star. The QPMs have m$_{K} \approx$ 6 to 9, similar to the expected m$_{K}$
for WR118, and featureless K-band spectra, also similar to WR118.
As a test of our hypothesis, we will obtain 
J-band spectra of the sources so that the classical emission-line spectra 
might be seen (Figer 1996).

\section{The Quintuplet and the Central Cluster}

     The Galactic Center emission-line stars have been regarded as
``exotic'' for their spectral characteristics in the K-band (Allen, Hyland
\& Hillier 1990; Krabbe et al.\ 1991; Libonate et al.\ 1995; Krabbe et al.\
1995; Blum, DePoy \& Sellgren 1995; Tamblyn et al.\ 1996). While other stars around the Galaxy
and in the Large Magellanic cloud are similar, the ensemble of stars in
the center, as a collection, is peculiar, but not unique. The Quintuplet
cluster contains many similar stars, as can be seen in Figure 2 and
FMM95.

     The WC9 stars recently found in the center (Blum, Sellgren \&
DePoy 1995; Krabbe et al.\ 1995) have counterparts in the Quintuplet
(here and FMM95-2). IRS16NE, which has LBV-like spectral characteristics
(Tamblyn et al.\ 1996), is similar to the LBVc in the Quintuplet
(FMM95-3). Some of the Ofpe/WN9 types in the center (IRS16 components)
are similar to q8,
q10 (Geballe et al.\ 1994; Figer 1995), and FMM95-1. IRS33E has a spectrum
similar to the ``OBI'' stars in the Quintuplet (Figer 1995; Najarro 1995;
Genzel et al.\ 1996). IRS7, the supergiant in the central cluster, is similar 
to q7 in the Quintuplet (Moneti, Glass \& Moorwood 1994).
Finally, the QPMs share similar spectral energy distributions (Okuda et 
al.\ 1990; Becklin et al.\ 1978)
and K-band spectra (Figer 1995) with the very red sources in the
Galactic Center, c.f. IRS8; both groups of stars may be DWCLs. This cursory 
comparison will be expanded in
Figer, McLean \& Morris (1996).


\begin{references}

\reference Abbott, D. C. \& Conti, P. S. 1987, \araa, 25, 113
\reference Allen, D. A., Hyland, A. R. \& Hillier, D. J. 1990, \mnras , 244,
706
\reference Becklin, E. E., Matthews, K., Neugebauer, G \& Willner, S. P.
1978, \apj, 219, 121
\reference Blum, R. D., Sellgren, K. \& DePoy, D. L. 1995, \apj, 440, L17
\reference Blum, R. D., DePoy, D. L. \& Sellgren, K. 1995, \apj, 441, 603
\reference Cohen, M. 1995, \apjs, 100, 413
\reference Cotera, A. S., Erickson, E. F., Colgan, S. W. J., Simpson, J.
P., Allen, D. A., Burton, M. G. 1996, preprint
\reference Figer, D. F., McLean, I. S. \& Morris, M. 1995, \apj, 447, L29
\reference Figer, D. F. 1995, PhD Thesis, University of California, Los Angeles
\reference Figer, D. F., McLean, I. S. \& Morris, M. 1996, in preparation
\reference Figer, D. F. 1996, in preparation
\reference Geballe, T. R., Genzel, R., Krabbe, A., Krenz, T. \& Lutz, D.
1994, in Infrared Astronomy with Arrays, I. S. McLean, Dordrecht:
Kluwer, 73
\reference Genzel, R., Thatte, N., Krabbe, A., Eckart, A., Kroker, H. \&
Tacconi-Garman 1996, \apj, submitted
\reference Glass, I. S., Moneti, A. \& Moorwood, A. F. M. 1990, \mnras, 242,
55P
\reference Hanson, M. M., Conti, P. S. \& Rieke 1996, preprint
\reference Harris, A. I., Krenz, T., Genzel, R., Krabbe, A., Lutz, D.,
Poglitsch, A., Townes, C. H. \& Geballe, T. R. 1994, in The Nuclei of
Normal Galaxies: Lessons from the Galactic Center, R. Genzel \& A.
I. Harris, Dordrecht: Kluwer, 223
\reference Krabbe, A., Genzel, R., Drapatz, S. \& Rotaciuc, V. 1991, \apj,
382, L19
\reference Krabbe, A., et al.\ 1995, \apj, 447, L95
\reference McGinn, M. T., Sellgren, K., Becklin, E. E. \& Hall, D. N. B.
1989, in IAU Symp. 136, The Center of the Galaxy, M. Morris, Dordrecht: Kluwer, 501
\reference McLean, I. S., et al.\ 1993, in Infrared Detectors and
Instrumentation, A. Fowler, Bellingham: SPIE , 513
\reference McLean, I. S., et al.\ 1994, in Instrumentation in Astronomy
VIII, D. Crawford, Bellingham: SPIE, 457
\reference Meynet, G. 1996, preprint
\reference Moneti, A., Glass, I. S. \& Moorwood, A. F. M. 1994, \mnras, 268,
194
\reference Nagata, T., Woodward, C. E., Shure, M., Pipher, J. L. \& Okuda,
H. 1990, \apj, 351, 83
\reference Najarro, F. 1995, PhD Thesis, Ludwig-Maximilian University
\reference Najarro, F., Hillier, D. J., Kudritzki, R. P., Krabbe, A.,
Genzel, R., Lutz, D., Drapatz, S. \& Geballe, T. R. 1994, \aap, 285, 573
\reference Okuda, H, Shibai, H., Nakagawa, T., Matsuhara, H., Kobayashi,
Y., Kaifu, N.,  Nagata, T.,  Gatley, I. \& Geballe, T. R. 1990, \apj, 351,
89
\reference Panagia, N. 1973, \aj, 78, 929
\reference Schmutz, W. 1996, private communication
\reference Schmutz, W., Leitherer, C. \& Gruenwald, R. 1992, PASP, 104, 1164
\reference Tamblyn, P. \& Rieke, G. H. 1993, \apj, 414, 573
\reference Tamblyn, P., Rieke, G. H., Hanson, M. M., Close, L. M.,
McCarthy, D. W. \& Rieke, M. J. 1996, preprint
\reference Timmermann, R., Genzel, R., Poglitsch, A., Lutz, D., Madden, S.
C., Nikola, T., Geis, N. \& Townes, C. H. 1996, preprint
\reference Vacca, W. D., Garmany, C. D. \& Shull, J. M. 1996, preprint
\reference Wainscoat, R. J. \& Cowie, L. L. 1992, \aj, 103, 332
\reference Williams, P. M., van der Hucht, K. A. \& The, P. S. 1987, \aap,
182, 91
\reference Yusef-Zadeh, F., Morris, M. \& van Gorkom, J. H. 1989, in IAU
Symp. 136, The Center of the Galaxy, M. Morris, Dordrecht: Kluwer, 275
\end{references}

\begin{figure}
\plotone{1.ps}
\caption{K-band spectra of WR stars in the Galaxy.}
\end{figure}

\begin{figure}
\plotone{2.ps}
\caption{K-band spectra of target stars in the Quintuplet.}
\end{figure}

\begin{figure}
\plotone{table1.ps}
\end{figure}

\end{document}