notes from the Leiden joint ALMA/HIFI calibration meeting. meeting occurred 2002Dec18-20. notes taken by BJB at meeting, and transcribed to electronic form on 2003Jan22/23. 2002Dec18 afternoon. plenary meeting on HIFI prepatory science. - Xander Tielens (HIFI project scientist) - "European prepatory science" www.astro.rug.nl/~european - FP6 ("Sixth Framework Program") announced yesterday. - lots of money. - little for this group though? - "Herschel Virtual Institute" -> will try for these funds? how does this relate to the "Herschel Data Centers"? - Herschel trying to combine with ALMA to go for these funds (science themes?). - they will try for money for organizing workshops, *not* for funding people/positions (this from Ewine). - proposals due end of april - Xander called for volunteers, and there were few. Ewine and Eric Herbst (interestingly) were the only two that agreed to help then and there. - how does this tie in with/compete with the AVO ("Astronomical Virtual Observatory" - the european equivalent of the NVO)? (this from Pierre Cox). - Pierre Cox (ALMA ASAC chairman) - "ALMA in FP6" possibilities: - build a "strong european network" - train young radio/mm/submm astronomers - develop software for science - develop ALMA advanced instrumentation (note BJB: how is this FP6 and not ALMA project?) - Software - Rx development - 2nd generation correlator - photonic LO (note BJB: again, this is a bit alarming! how is this coordinated with the project and work therein?) will try to extend RADIONET to the mm/submm communities (get a coordinated presence therein, which has been lacking). - Thomas Giesen - "Molecular Spectroscopy" conclusions of preparatory science workshop in october '01: - get organized - find funding - name molecules of interest groups formed since (or highlighted since): - European Associated Laboratory for High Resolution Molecular Spectroscopy (HiRes) - Cologne Database for Molecular Spectroscopy (CDMS) molecules of interest: - light hydrides (e.g., CH2) - non-polar, low bending mode molecules - ions - water & relatives (is a light hydride, but important enough to separate out, IMHO) lots of good recent lab results because of "Quantum Cascade Lasers" - Evelyne Roueff - "Molecular Excitation" effort: - electron impact studies (note BJB: do they have ammonia???) - new results on H2O-H2 collisions - database for molecular excitation (note BJB: NH3 + He - Hodges & Wheatley, J Chem Phys, 114, 8836, 2001) electron impact: "short range effects" important for deltaJ=1 transitions? have a look at: www.strw.leidenuniv.nl/~moldata also: basescol.obs-besancon.fr also: ICAMDATA - Adam Walter/Sven Thorwirth - "Databases/Webtools" AW portion: lots of different databases to handle: CDMS, NIST, JPL, HITRAN, etc.. no single one has everything that Herschel needs. how to solve? 1 - incorporate existing dBs into 1; 2 - just have pointers to the appropriates ones. unclear which way to proceed. measurements are (relatively) sparse from 500 GHz to 2 THz. look at: PCMI; Astrospec; CASSIS (?) ST portion: CDMS (www.cdms.de) - compare to NIST & JPL. currently 166 entries. same layout as JPL dB. - Ewine van Dischoek - "Spectral Line Modeling" old way: - constant Tex - rotation diagrams - escape probability for constant T,n need more complete treatment, of course. iterate between physical model and observed spectrum, using a more complete description of the physics: __________________________ | _________ | | | | | | | \/\/ |\/ | n(r) -----> T(r) -----> x(r) -----> line spectra ^ ^ ^ | | | thermal chemistry rad balance xfer + telescope parms Monte Carlo codes for rad xfer: Barnes 1979; Choi et al. 1995; Jurela 1979; Park & Hong 1998; others... Lambda Acceleration: Rybicki & Hummer 1991; Dullemond & Turolla 2000; Hogerheide & van der Tak 2000; others... www.strw.leidenuniv.nl/~radtrans comparison of 7 1-D radiative transfer codes: van Zanderoff et al. see at: www.strw.leidenuniv.nl/~radtrans/radtrans.ps differences up to 20% or so seen for more complicated case. and large differences in the structure as a function of radius. gridding is a big issue. need good rate coefficients. - Maryvonne Gerin - "Ground-based Observations" "template sources" (note BJB: what are these???) (note BJB: this seems like it can be done already, just as a natural consequence of research of interested scientists. i don't see a need for a special "program" to do this, unless specific prior ground-based observations are required to calibrate the instrument. and this wasn't shown (to my satisfaction)...) - Serena Viti - "Chemical Models" model characteristics: - time dependent - depth dependent - gas-grain/gas chemistry - degrees of freedom: - elemental abundances - T - rho - radiation field - cosmic ray ionization rate - dynamical 'switches' (simulate shocks, e.g.) - chemical reactions (number, type, & rates) - depletion (freezing out) current group: Charnley, van Dishoeck, Herbst, Le Bourlot, Millar, Viti need to benchmark current codes (compare results on a simple and more complicated model - similar to what the rad xfer group did). "regions of interest" for Herschel: - ISM - hot cores - circumstellar/protoplanetary disks - outflows/jets - shocked regions www.star.ucl.ac.uk/~sv/ChemMod/home.html -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2002Dec19 morning. - Frank Helmich - "Herschel/HIFI Overview" HIFI launches in 2007/2008 HIFI: 22 institutes contributing ICC = "Instrument Control Center" (where all the calibration work is being done). PACS = 40 um - 200 um SPIRE = ? HIFI = two different receiver bands: 480-1250 GHz; 1410-1910 GHz. SIS mixers in 480-1250; HEB in 1410-1910. delta f = 0.14 MHz min; 1 MHz typical total bandwidth = 4 GHz single linear polarization 80 K ambient absolute calibration accuracy: 10% spec; 3% goal. 2-load calibration system. extensive documentation (2 years effort already, and well documented, including control),. "use cases" are critical. this is "ESA speak"... - Carsten Kramer - "Beam Pattern on Herschel" geometric obscuration = 8% primary accuracy = 3 um surface rms (6 um path-length error) OTFM? yes. but crude. beam-switching: 3' throw. - Volker Ossenkopf - "HIFI Observing Modes and Calibration Plan" 2.7 m primary diameter (effective) -> 13" to 40" resolution (FWHM) major problems: - sideband gain ratio - is it stable over time? - slew times are long: t = 10 + sqrt{delta theta) seconds where delta theta is in arcseconds - standing waves two-load chopper to calibrate Rx. 1 @ 15K, 1 @ 100 K. they will attempt to use OFF pos'n to "calibrate" the standing wave contribution. BUT, this won't work at the high band. ALSO - Pepe Cernicharo points out that the OFF calibration doesn't work for calibration standing wave problem, at least for Earth-based telescopes (they tried it at the 30-m?). Volker argues that this is an atmosphere problem. some uncertainty and disagreement on this... cal cycle example: 2,1,2,1,2,1,2,1,2,3,2,1,2,1,2,1,2,1,2,3,2,1,2,1,2,1,2,1,2,3,4,2... 1 = source 2 = "reference" 3 = hot-cold load cal 4 = standing wave cal 2,1,2,1... = "reference loop" 2,3,2 = "bandpass calibration loop" 2,3,4,2 = "standing wave calibration loop" loop times determined by combination of thermal rms and gain drift. current thinking is ~100 sec for bandpass cal loop; ~1000 sec for standing wave cal loop. Jesus-Martin Pintado points out problem in knowing or measuring the coupling coefficients. HIFI calibration URL for maillist: mail.ph1.uni-koeln.de/cgi-bin/mailman/listinfo - Maryvonne Gerin/David Teyssier - "Astronomical Calibration Sources for HIFI" (talk given by DT). distinguish between "photometric" vs "spectrometric" vs "instrumental" calibrators... visibility is a problem - they are at L2 orbit point, and can't look "back" at the Earth/Sun direction. so, need good set of secondaries and monitoring. problem of variation timescale of secondaries though. Mars models - Griffin, Lellouch Uranus model - Moreno asteroids - Muller (but SPIRE driving this) evolved stars - Loup et al. 1993 need ground-based observations of secondaries (tough at these frequencies though). which telescopes? CSO. others? APEX, ASTE, JCMT, etc... they can post-correct amplitude scale, if new absolute values are available. - Stephane Guilloteau - "ALMA Calibration Issues" see Stephane's presentation on ALMAEDM. - Bryan Butler - "Astronomical Calibration Sources for ALMA" see Bryan's presentation on ALMAEDM. ------------------------------------- afternoon. - John Conway - "ALMA Configurations" summary of status. "made some mistakes" on 4 or 5 pad positions. not given enough time (10 days after new map reception), & didn't know whether to adopt conservative or more agressive stance WRT slope mask... now working on the reconfiguration scheme. Stephane prefers a more dynamic reconfig scheme ("reaction to proposal pressure"). some disagreement on this amongst the audience... - All - science IPT milestone discussions big problem with Juan-Ramon Pardo not being able to contribute effort. lots of discussion on how to proceed. big problem with polarization. seems to be the one place where we have expended little effort to this point, and we have no person assigned to this currently (Steve Myers was going to take it over, but with his new position as AIPS++ project scientist, this will likely not happen). can we find somebody else to take over this effort? -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2002Dec19 morning. - Stephane Guilloteau - "Calibration Requirements with Science Examples" Tatematsu - need beam error pattern Wilson & Matthews - what is best freq. for thermal (& faster, since dust goes like nu^3) observations? .5-5% pol'n with SNR of 5-10. (note BJB: *too squishy*!) Stephane - this specs differential gain stability on the 2 poln's of the Rx. 5 X 10^-4 ? more demanding: SD inclusion. need to know pol'n angle to 6 deg. (note BJB: where does 6 deg come from?). French SIMS (even with ACA) indicate that this will be extremely difficult. van Dischoeck & Blake - only _relative_ amplitude calibration between receiver bands is needed. "few" %. (really 5%, after discussion). line survey - can we deconvolve sidebands? (note BJB: this would just be like a 3-D deconvolution...). need a req. on sideband gain ratio stability for this. Peter Schilke will provide a number for this. Momose - really tough BP cal example. 1 part in 1000 or so, but absorption in front of a strong quasar (so no stronger astronomical BP sources). Gurwell - Mars atmosphere lines. similar problem to Momose. interesting that there were no examples for flux density absolute scale. from discussion - 5% might be OK? for comparison with other wavelength instruments. also got no examples on, e.g., ant. beam props or pointing. Stephane considers these current specs to be OK and defended (historically), so specifically asked the ASAC for examples on pol'n and BP. afternoon. - Stephane Guilloteau - "ALMA Bandpass Calibration" (note BJB: seems to be advocating calibrating bandpass @ different frequency than observing? how can this be, when atmosphere and antenna are changing as fn. of frequency? - i must be missing a step here where the atmospheric and antenna part are done...). presentation of idea on "bandpass normalization" (at least that's what we call it in VLA parlance) - i.e., calibrating the bandpass with the autocorrelations. note that this will be in trouble if you have any strong line in the bandpass (including RFI). we've had only mixed results with it at the VLA, and although it's available, it's not often used... - Aurore Bacmann - "ALMA Bandpass Calibration, more..." this was originally supposed to be a talk on bandpass cal. on astronomical sources (at least i thought it was), but it turned out to be a presentation on standing waves. very nice, but not what i was expecting... v_ripple = c / 2D ~ 30 MHz for ALMA antennas amplitude is proportional to wavelength (worse at long wavelength). very nice work on simulating the standing wave problem in the ALMA antennas, full physical optics treatment. simulated/calculated results on standing wave ratio: - straight subreflector 0.7% - with absorbing disk 0.7% - with tangent cone 0.08% - with discontinuity (hole in subreflector) 1.3% - with scatter cone (even inside hole) 0.8% so, interestingly, cutting a hole in the subreflector is actually worse than just leaving it there (in terms of standing wave). Richard Hills says he's known this for a long time and tried to convince Jack Welch of this, to no avail. even with a scatter cone inside, it's just as bad as the plain subreflector. problem with tangent cone is that optimal angle is such that some of the subreflector actually gets blocked off - solution is maybe to taper tangent cone. Kate Isaak points out that maybe we could do the single dish trick of modulating the subreflector in/out position by +- 1/8 wavelength to get around this. (note BJB: this didn't come up at the meeting, but after the fact, it occurs to me that this would be nearly impossible since you'd probably have to synchronize?) Stephane thinks that because of this study, there is no need to further simulate the layout, etc... of the dual-load in the subreflector cal. system. - Stephane Guilloteau - "Semi-transparent Vane" Richard Hills points out that the dual load *doesn't* suffer from the problem of needing to know the opacity (at least any more than the semi-transparent vane does), because you can think of it as a single load, which doesn't depend so strongly on opacity, *plus* additional info. are we just not looking at this in the right way? Jesus-Martin Pintado points out that semi-transparent vane is *only* needed to avoid saturation. but he also points out potential serious problems with polarization. also difficult to actually measure. JMP will attempt to measure it to 3% or so this spring (see next talk). Stephane and Richard both point out that if the spec is relaxed to 5% (or even maybe 3%), that there is absolutely no need to go with a fancy dual-load or semi-transparent vane calibration system, just use a simple ambient load. it was felt that we could slip the spec on the mechanical design of the dual-load in the subreflector, based on results already known now. - Jesus-Martin Pintado - "Semi-transparent Vane Test Plans" also involved: S. Navarro, M. Carter (IRAM); some others. to be done at the IRAM 30-m antenna. 3mm and 1.3mm Rx's simultaneously. the material is a 1cm thick foam. transmission = 90%, but they will measure it (with 0.5% accuracy), as a function of frequency. they will attempt to measure polarization effects (to 0.8%). they will attempt to measure Tvane, to 3%. Richard points out that you want to vary the physical temp. of the vane, to get a good test. also, will attempt to measure standing waves - this could be a serious problem. they will compare results to what is already used on the 30-m: dual-load and single-load chopper wheel methods. they will attempt to do this during the spring, but time is not formally allocated to them, so they are at the whims of the IRAM scheduling. Jesus thinks that they might do the observations as early as Feb., but this is optimistic. they might attempt to do measurements with a lab mock-up of the Rx system, at least as much as they can. - Juan-Ramon Pardo - "ATM" they did one WVR test in 2002 at CSO/JCMT (he and Martina Wiedner). coupling of the WVR to the atmosphere is only ~ 63%! new measurements go up to ~1.6 THz. new modelling of the continuum to go > 1 THz. nu^2 dependence @ nu<900 GHz starts to break down @ 1.5 THz. phase correction tests on SMA in March 2002. observed Uranus. 230 GHz. results not so good (in terms of WVR variation matching observed interferometric phase)! want to do more tests, but a problem - can't get time on telescopes, and Martina is no longer at SMA. ATM tasks in 2002: - code cleaning - separating code levels - improved speed - ATM library for ALMA - interfacing to other software done under the auspices of ADACE - "ALMA Data Analysis Center in Europe". hmmm.... wierd that it's separate from normal ALMA software and science effort. software includes 183 GHz WVR fitting. (note BJB: this should be used to look at site 183 GHz radiometer data!). some discussion on the profile of O3. i thought this was pretty well characterized? has been modelling hydrometeors - both liquid and solid. have an array simulator (see talk by Francois later). can have full 2-D phase screens (not fully 3-D, except that you specify whether they are thin or thick, i think) which move over the array. - Kate Isaak - "WVR" spec = 10 (1 + PWVmm) um in 1 second (1-sigma) 1 deg in elevation... two options: - Dicke switch (DSB) - correlation receiver (SSB) 4 IF chains: IF nu-nu0 delta nu 1 0.96 0.16 GHz 2 1.94 0.75 3 3.175 1.25 3 5.20 2.50 giving up on correlating backend (a'la Andy Harris) [ also, a group at Cambridge has a wider bandwidth version - Richard had a work package request to look at using it for the WVR but it wasn't funded, unfortunately... ] - Richard Hills - "WVR, more" what is the test plan? Richard thinks that testing it at the ATF is best. requires an interferometer, of course. he would like to have it available to have WVRs on it by early 2005. two options: - analytical (e.g., ATM) fitting - emperical model & adjust over time (e.g., neural nets) possibility of doing tip-tilt correction. rotating mirror or prism, or chopping to antenna quadrants (@ ~ 10 Hz). but, should he pursue this? should he try to get a student to look into it/work on it? should it go in the proposal? unclear. mixed reaction to it. - Francois Viallefond - "ALMA Simulations" 2 pieces: - Obs Tool (which is also a Prop Tool). relatively simple, with uv coverage + model + simulate) - full-blown stand-alone simulator GIPSY & GILDAS versions SIMULATM (in GIPSY). combination of simulation + ATM (Juan-Ramon and Francois). done under auspices of ADACE (note BJB: this ADACE seems to me to be a problem - it's s/w development outside the normal routes, and is taking up alot of science IPT potential resources - it includes Gueth, Pety, Viallefond, Guilloteau, Cernicharo, Pardo, Lucas, at least. note that the only reason that Pardo delivered ATM for SIMULATM [and helped integrate it] was because of a signed contract to do so with this ADACE. perhaps the science IPT should ask for a separately signed contract to deliver ATM software for our use, since it now appears that otherwise we will not get it.) full-blown simulator with turbulent screen. very nice. simulates visibilities & WVR observations, and the correction of the vis with the WVR observations (WVR fitting, etc...).