Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 4416c Report Date: 09-May-96:19:36 Version: ********** Check-in Date: ********** 1.Proposal Title: THE HOT STELLAR COMPONENT IN THE CENTERS OF M31 AND M32: CYCLE3 HIGH ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID GALAXIES & CLUSTERS GO Sub Category STELLAR POPULATIONS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Henry C. Ferguson UNIVERSITY OF CAMBRIDGE ENGLAND ------------------------------------------------------------------------------------ 7. Abstract We propose to construct a far-UV color-magnitude diagram for the point sources detected in FOC images of the centers of M31 and M32. These data will be used, in conjunction with spectroscopy obtained by the Hopkins Ultraviolet Telescope, to provide constraints on the mix of stars responsible for the far-UV emission in old, metal-rich stellar populations. Our inference from the existing HUT and FOC data is that the resolved sources are mostly low-mass PAGB stars. If so, our observations will provide the first direct estimates of the PAGB star mass distribution, and will provide important insight into the differences in the evolution of the stellar populations in these two galaxies, the amount of mass-loss among the AGB progenitor stars and evolution along the PAGB. By combining our observations through different filters, we will be able to assess the emission-line contribution and search for variability. Comparison with the HUT data will allow a precise estimate of the contribution to the far-UV light from PAGB stars of different mass, and will allow a more precise determination of the spectral-energy distribution of the remaining unresolved population. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 11.64 par: 0 10. Num targs pri: 2 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: FOC ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 4416c PI: Henry C. Ferguson Proposal Title: THE HOT STELLAR COMPONENT IN THE CENTERS OF M31 AND M32: CYCLE3 HIGH ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Pi Henry C. Ferguson UNIVERSITY OF CAMBRIDGE UNITED KING X Ivan R. King UC-BERKELEY USA Arthur F. Davidsen JOHNS HOPKINS UNIVERSITY USA S. Adam Stanford UC-BERKELEY USA Jean-Michel Deharveng CNRS LABORATOIRE D'ASTRONOMIE FRANCE X SPATIALE ------------------------------------------------------------------------------------ 3. Description of proposed observations. The FOC will be used in f/96 mode with the F275W and F175W filters in zoom mode (0.022 X 0.044 arcsec pixels) to obtain images of the M31 bulge and of M32 in the far UV. We strongly prefer to use f/48 mode if it becomes available again for imaging. We originally proposed to obtain photometry accurate to 10% in the F150W and F220W filters to the detection limit of the existing f/48 F175W image. This is not possible in the f/96 mode. Instead, we aim to obtain F275W images sufficient to get S/N ~ 10 on a T=20000K star with STMAG=21 in the F175W bandpass. The additional shorter F175W exposures will be combined with the existing f/48 F175W images to obtain nearly the same S/N, and will also serve to test the calibration. We wish to keep the orientation the same as the previous f/48 F150W observations, so that we do not lose stars off the corners of the field. Note that if the observations are to be carried out in f/48 mode, some of our requirements will change, and this could potentially affect the scheduling of the observations. In particular, the ORIENTations will likely be different, and we would require DARK time for F150W observations. Page 3 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. The stars we propose to observe are detectable only in the far-UV. The integrated spectra of M31 and M32 have been measured by IUE \acite{Johnson79; Welch 1982; Burstein 1988}. M31 was observed by by HUT \acite{Ferguson 1991 ApJ; Ferguson Davidsen submitted}. Low-resolution far-UV images were obtained from a sounding rocket \acite{BCHHOS85} and more recently from the UIT \acite{O'Connell 1991 Stellar; O'Connell 1992 ApJ}. No resolved sources were detected in these images. Far-UV images have been taken in 1991 with HST. In the M31 F175W image \acite{King 1992 ApJ}, 137 sources were detected in the $44 \times 44\arcsec$ FOC $f/48$ field of view. Estimates from this image suggest that resolved sources provide roughly 15\% of the total flux at 1750\ang. More recent images were obtained at 1500\ang with the F130LP+F150W filters \acite{Bertola 1992}. These images were not as deep as expected, and the field of view was $22 \times 22\arcsec$, so fewer sources were detected. Preliminary estimates from these images suggest that the resolved sources contribute a much larger proportion of the far-UV flux \acite{Buson 1992}. While we expect the FOC calibrations now planned for Cycle 2 to resolve much of the discrepancy about the contribution of the resolved sources to the total far-UV flux, the wavelength coverage and depth of the existing images is insufficient to constrain the temperature distribution of the point sources and the amount of emission-line contamination. A color- magnitude diagram with a wide UV baseline will provide the necessary constraints, and will allow for the first time a direct estimate of the PAGB star mass distribution. For comparison with the existing F175W image, there is are great advantages to to carrying out these observations in f/48 mode if it becomes possible to do so. To measure the PAGB-star mass distribution (assuming that is what most of the sources are), we will try to assign stars to evolutionary tracks like those shown in Fig. 3. To do this adequately for a large enough sample, we desire photometric accuracy better than 0.1 mag down to an ST magnitude $m = 21.0$. This should be sufficient to probe the mass distribution down to the Schoenberner 0.546 solar-mass track, and should allow detection to even lower masses. It is not possible to achieve this desired sensitivity in f/96 mode within the time allocated by the TAC. In f/96 mode, the best combination of temperature discrimation and sensitivity can be obtained by using the F275W and F175W filters. The F175W observations will serve to calibrate and increase the S/N of the existing f/48 images. The F175W images are not quite as deep as the F275W images. The ingredients in the exposure time calculation are as follows: Source spectral Energy distribution: - We have used a Kurucz (1992) model atmosphere with T_eff = 20000K and log(g) = 4.5. For a source of this temperature detected at 1 count/s in the f/48 F175W filter, the count rate would be 1.25 and 3.02 in the f/96 F175W and F275W filters, respectively. Diffuse UV background + redleak: - For M31 we used a spectral-energy distribution compiled by Burstein (1992); for M32 we used the IUE SED from Burstein (1988), joined at 3300A to the "cold-E" 15Gyr model of Rocca-Volmerange & Guiderdoni (1987). To normalize, we estimated the mean background (after subtracting dark-count) within the central 15 arcsec diam (3.2e-3 counts/pixel) for M31; 2.9e-3 counts/pixel for M32). Folding through the SYNPHOT-generated response functions, gives 1.15e-3 counts/pixel in the F175W filter and 8.71e-3 counts/pixel with F275W for M31. For M32, the background is 1.13e-3 and 1.30e-2, respectively. Airglow + detector background: - For 90 degree solar zenith angle, Fig. 41 of the FOC Instrument Handbook gives 2.0e-2 counts/pixel with no filters. The resulting rates using the filter transmissions at Ly-alpha from SYNPHOT are 2.0e-3 and 5.9e-7 through the F175W and F275W filters, respectively. Detector background (dark count) was taken to be 6e-4 counts/pixel. Exposure times were calculated using equation 1 of section 6.0 in the FOC Instrument Handbook. While profile fitting will be used to do the photometry in the real data, for our purposes here we computed the exposure times for stars measured through apertures of the sizes given in the different rows of Table 9, and chose the aperture with the shortest exposure time. In the Table below, R_S_tot is the count rate for a source with an ST magnitude of m_F175W = 21 in the f/48 F175W filter, integrated over the entire PSF, R_B_tot is the total background in counts/pixel, and R_S and R_B are the source and background count rates in a 0.176 arcsec radius aperture. RESULTS OF EXPOSURE TIME ESTIMATE Galaxy Filter R_S_tot R_B_tot R_S R_B Exposure (sec) M31 F175W 0.24 1.9e-3 0.11 0.57 16000 M31 F275W 0.58 9.3e-3 0.13 0.45 11000 M32 F175W 0.24 1.9e-3 0.11 0.54 16000 M32 F275W 0.58 1.4e-2 0.13 0.61 16000 We were granted 14.62 hours of spacecraft time by the TAC. We must therefore shorten exposure times, and choose to do so in the F175W filter, where we can get some S/N back by combining with the existing f/48 images. We put more time on M31 because the existing f/48 image is slightly lower qualitiy than the M32 image due to defocussing in the detector. The exposure times shown in the exposure log section reflect these modifications of the exposure times times shown in the above table. Page 4 ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. For both the F175W and the F275W exposures, we wish to use the same orientation as the previous FOC F150W observations. This is to avoid losing stars off the corners of the field. The desired orientations are 97D for M31, and 98D for M32. Our pointing positions are chosen to be the same as those of the FOC F150W observations (program ID 2719). Our f/96 22x22" field with thus include all the stars in the F150W f/48 22x22" field. (The existing f/48 F175W images were taken in zoom mode, and completely include our proposed f/96 field.) Our orientation requirements and pointing positions would change if we were allowed to use f/48 mode, because we would then like to align the new images with the existing F175W images, rather than the existing F150W image. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. Data will be reduced at Berkeley using the same procedures that were used to analyze the F175W image. Source detection will be carried out by eye and using DAOFIND. Photometry will be performed on the un-deconvolved images using DAOPHOT. Standard monte-carlo procedures will be used to estimate completeness. Both images will be deconvolved to look for extended emission that might be indicative of planetary nebulae. Color-magnitude diagrams and color-color diagrams will be be compared to models constructed from theoretical evolutionary tracks, using stellar model atmospheres to predict the far-UV fluxes. Spectral-synthesis software developed by HF for analysis of the HUT data has been modified to produce the evolutionary tracks shown on Figs. 2 and 3 of this proposal. Modifications now underway for further analysis of the HUT data and analysis of the proposed FOC data include incorporating a realistic spread in metallicity, providing for different enrichment of metals relative to helium, allowing different mass-loss laws on the RGB and AGB, and incorporating improved non-LTE model atmospheres for stars hotter than T_eff = 35000 K. Improved evolutionary tracks will be incorporated as they become available. Software developed independently by JMD is being used to model the luminosity function in the F175W image. The results from the separate models will be compared in the near future. A rough division of resonsibilities is as follows: HF is responsible for coordinating the overall effort, IK and AS provide expertise on the FOC and will be responsible for the initial data reduction and photometry. AFD provides expertise on the HUT data. HF and JMD are responsible for modeling the resulting color-magnitude diagram, although all will assist in its interpretation. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. Page 5 ------------------------------------------------------------------------------------ 9. Description of previous HST work. King and Deharveng are on the FOC IDT; Davidsen is on the FOS IDT. The complete list of observations for these teams can be found in documents readily available. The direct precursor to this proposal is FOC-3105 UV IMAGING OF THE CENTERS OF M31 AND M32 Observations possibly related to this proposal include SAO-3121, MORPHOLOGY OF FAINT GALAXIES - PART II GTO-1277, IMAGING OF M31-GROUP GALAXIES GTO-1278, SPECTROSCOPY OF THE CENTERS OF M31, M32, AND NGC 205 GTO-1279, STRUCTURE OF GLOBULAR CLUSTERS GTO-1281, THE FAINT POPULATION IN BAADE'S WINDOW GTO-3218, (continuation of 1279) GTO-3219, (continuation of 1277) GTO-3325, (continuation of 1279, 3218) AUG-3684, IMAGING OF GLOBULAR CLUSTERS AUG-3685, IMAGING OF HIGH-REDSHIFT FIELD GALAXIES AND CLUSTERS AUG-3870, IMAGING IN THE M31 GROUP GTO-4138, IMAGING OF NGC 4472 GO-3647 THE STAR-FORMING HISTORY OF ELLIPTICAL GALAXIES The GO program is a Cycle-2 program of FOS spectroscopy with Ferguson as PI and Davidsen among the Co-I's. 3105 revealed PAGB stars in the center of M31 and showed that they account for only a small part of the UV upturn. M32 (in 1277) went into Crane et al., below, which found that none of the ellipticals observed so far have isothermal centers. ``The Current Ability of HST to Reveal Morphological Structure in Medium-Redshift Galaxies'', King, I.R., et al. (8 other authors), Astron. J. 102, 1553, 1991. ``Preliminary Analysis of an Ultraviolet HST FOC Image of the Center of M31'', King, I.R., et al. (19 other authors), Ap. J. Letters, 397, L35, 1992. ``FOC Observations of Galaxy Cores'', Crane, P.C., et al. (19 other authors), submitted to A. J. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). HF is funded by an SERC rolling grant for observational astronomy, through September 1993. Destination thereafter is likely STScI. Computing facilities at Cambridge include four SUN-4 computers dedicated to HST projects, with a total of 6 Gigabytes of disk storage, and exabyte cartridge tape systems for off-line storage. Each SUN has at least 24 Mb of core memory and three have i860 array processors to speed up image deconvolutions. These machines operate within a larger network of SUNs that can be used for HST data analysis as well. An extensive suite of software is installed on the SUNs, including IRAF, STSDAS, FIGARO, VISTA, and MEMSYS5. These systems are maintained by an in-house support staff funded by STARLINK. The data reduction facilities used by members of the FOC GTO team at Berkeley are available for this project. This includes four SPARCstation IPC's with 3 gigabytes of disk space dedicated to HST work. ------------------------------------------------------------------------------------ 11. Address Information Name: HENRY C. FERGUSON Category: PI Institution: University of Cambridge Address: THE OBSERVATORIES, MADINGLEY ROAD City: CAMBRIDGE State: Zip Code: CB3 0HA Country: UNITED KINGDOM Telephone: (0223) 337548 Telex (or e-mail): 817297 ASTRON G ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 4416c [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC224 M31 E,301,910,913 RA = 00H 42M 44.90S +/-1", 2000 EXT 1 SURF(V)=15.75 ANDROMEDA DEC = +41D 16' 08.0" +/-1" 2 F(1750)=1.45E-17 GALAXY 3 SURF-CONT-BKG(1750)=1.02E-16 Comments: FLUX 2 IS ST MAG = 21, OUR DESIRED LIMIT FOR 10% PHOTOMETRY. FLUX 3 CONVERTS THE OBSERVED F175W MEAN BACKGROUND OF 3.2E-3 CTS/S/PIX BACK TO A FLUX. THE BACKGROUND IN F/96 F175W AND F275W ARE ESTIMATED IN QUESTION 4 OF THE GENERAL FORM. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC221 M32 E,303,910 RA = 00H 42M 41.71S +/- 1", 2000 1 SURF(V)=15.77 DEC = +40D 51' 54.1" +/- 1" 2 F(1750)=1.45E-17 3 SURF-CONT-BKG(1750)=9.2E-17 Comments: FLUX 2 IS ST MAG = 21, OUR DESIRED LIMIT FOR 10% PHOTOMETRY. FLUX 3 CONVERTS THE OBSERVED F175W MEAN BACKGROUND OF 2.9E-3 CTS/S/PIX BACK TO A FLUX. THE BACKGROUND IN F/96 F175W AND F275W ARE ESTIMATED IN QUESTION 4 OF THE GENERAL FORM. ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 4416c [ 7] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC224 FOC/96 IMAGE 512X102 F175W PIXEL=50X25 1 9199S 3 CYCLE 3 4 ORIENT 97D +/- 5D Comments: ORIENT REQUIRED TO KEEP SAME STARS AS PREVIOUS F150W OBSERVATION. IT IS PERMISSIBLE TO INCREASE ORIENT BY 90D OR 180D. WOULD LIKE TO HAVE AT LEAST THREE SUBEXPOSURES READ OUT IF SCHEDULING ALLOWS. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC224 FOC/96 IMAGE 512X102 F275W PIXEL=50X25 1 11396S 1 CYCLE 3 4 SAME ORIENT FOR 2 AS 1 Comments: ORIENT REQUIRED TO KEEP SAME STARS AS PREVIOUS F150W OBSERVATION. IT IS PERMISSIBLE TO INCREASE ORIENT BY 90D OR 180D. WOULD LIKE TO HAVE AT LEAST THREE SUBEXPOSURES READ OUT IF SCHEDULING ALLOWS. ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC221 FOC/96 IMAGE 512X102 F175W PIXEL=50X25 1 4599S 4 CYCLE 3 4 ORIENT 98D +/- 5D Comments: ORIENT REQUIRED TO KEEP SAME STARS AS PREVIOUS F150W OBSERVATION. IT IS PERMISSIBLE TO INCREASE ORIENT BY 90D OR 180D. WOULD LIKE TO HAVE AT LEAST THREE SUBEXPOSURES READ OUT IF SCHEDULING ALLOWS. ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC221 FOC/96 IMAGE 512X102 F275W PIXEL=50X25 1 16000S 2 CYCLE 3 4 SAME ORIENT FOR 4 AS 3 Comments: ORIENT REQUIRED TO KEEP SAME STARS AS PREVIOUS F150W OBSERVATION. IT IS PERMISSIBLE TO INCREASE ORIENT BY 90D OR 180D. WOULD LIKE TO HAVE AT LEAST THREE SUBEXPOSURES READ OUT IF SCHEDULING ALLOWS. ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 4416c [ 8] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOC/96 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters PIXEL=50X25 ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 11.64 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category GALAXIES & CLUSTERS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category STELLAR POPULATIONS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 3; ORIENT 97D +/- 5D; SAME ORIENT FOR 2 AS 1 ORIENT 98D +/- 5D; SAME ORIENT FOR 4 AS 3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F175W F275W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC224 M31 ANDROMEDA GALAXY NGC221 M32 ------------------------------------------------------------------------------------------------------------------------------------