Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5722 Report Date: 18-Jul-95:17:53 Version: ********** Check-in Date: ********** 1.Proposal Title: PAGB STARS IN ELLIPTICAL AND BULGE-DOMINATED NEARBY GALAXIES -- CYCLE 4 CARRYOVER ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID STELLAR POPULATIONS GO/CAR 4240 Sub Category OLD FIELD STARS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Prof. Francesco Bertola DEPARTMENT OF ASTRONOMY PADU ITALY +39-49-661499 PROF. OF ASTRONOMY ------------------------------------------------------------------------------------ 7. Abstract We propose to search for the stellar population which produces the far ultraviolet rising branch from 1200-1800 A in the spectral energy distributions of early-type galaxies. One of the most likely sources of this hot emission are evolved post- asymptotic giant branch (PAGB) stars. We estimate that the brightest PAGB stars at the distance of M31 can be unambiguously detected using the far-UV imaging capabilities of HST+FOC. The possible presence of other kinds of hot stellar components that could contribute flux to the rising branch (e.g. young stars, accreting white dwarf stars in binaries) can also be detected in these images, as they will be intrinsically brighter than PAGB stars, but less numerous. If the source of this far -UV flux is PAGB stars, their absolute magnitudes in galaxies of different mean metallicities are critical tests of current theories of PAGB evolution. ------------------------------------------------------------------------------------ 8. Scientific Key Words: PAGB STARS, POPULATION II, ELLIPTICAL GALAXIES, UV IMAGING ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 2.0 par: 0 10. Num targs pri: 3 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: FOC ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5722 PI: Prof. Francesco Bertola Proposal Title: PAGB STARS IN ELLIPTICAL AND BULGE-DOMINATED NEARBY GALAXIES -- CYCLE 4 CARRYOVER ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Prof. Francesco Bertola DEPARTMENT OF ASTRONOMY PADUA ITALY X UNIVERSITY Dr. David Burstein ARIZONA STATE UNIVERSITY USA Dr. Lucio M. Buson ASTRONOMICAL OBSERVATORY PADUA ITALY X Prof. Cesare Chiosi DEPARTMENT OF ASTRONOMY PADUA ITALY X UNIVERSITY Dr. Sperello Di Serego Alighieri ARCETRI ASTROPHYSICAL ITALY X OBSERVATORY ------------------------------------------------------------------------------------ 3. Description of proposed observations. We propose to image the central regions of M31, M32 and NGC 205 by using the FOC in the F/48 configuration. We need to image each target using the far-UV filter F150W. To avoid problems related to the disuniformity in the response and defect in the photocatode, we are requesting that two images (about one hour each) be obtained for each galaxy, in order to provide reliable number counts of faint UV- bright stars (a critical test of the new PAGB models). The F150W filter isolates the spectral region where PAGB stars are relatively the brightest, and where the galaxy background is very low. The bulge of M31 is an object of high metallicity for which we expect about 200 bright PAGB stars within the F/48 aperture. Fewer bright PAGB stars are expected in M32 (about 20), both from the known lower UV flux in that galaxy, and from the lower metallicity. The fewest PAGB stars are expected to be found in NGC 205, but blue horizontal branch stars could be present if there is a wide mix of metallicity in this galaxy. In addition, the presence of known, ongoing star formation in NGC 205 could contribute significant numbers of main sequence, stars even in regions without obvious star formation. In all cases we expect to detect individual stars in these galaxies, of which both the luminosities and the number will be important to this study. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. To detect bright PAGB stars (Mv about +1) in external galaxies it is necessary to operate in the far-UV (both where they emit their largest flux, and at which they are more easily discriminated against redder stars) with a large telescope, since they are faint (mv > 25). High angular resolution is necessary to isolate crowded objects against a non negligible background. The observations here proposed represent a one of the final goals of a long term project carried out by the proposers both from space (IUE) and from the ground (Lick Observatory), as well through theoretical modelling of the late stages of stellar evolution. Page 3 ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. Our estimate of the exposure times with the aberrated HST is based on the following ingredients: 1. We require a 10% photometric accuracy (S/N=10) for a PAGB star at the knee of the slowest of the Schoenberner (1983, Ap.J. 272, 708) evolutionary tracks (M_core=0.546M_o, log L/L_o=2.95, log T_e=4.93, hereafter our reference PAGB star) and a clear detection (S/N=5) for a PAGB star which is one magnitude fainter. 2. We concentrate on the F/48 + F150W combination, which gives the best contrast between the hot stellar population and the underlying cold stars. 3. We use the measured FOC PSF in the UV and in particular the fact that 15% of the PSF flux is contained in the central 13 pixels (radius of 0.09 arcsec). This core is the important part of the PSF for the detection and measurement of faint point sources. 4. We consider the following components of the background: the detector background as measured in orbit (0.0019 cnt/s/pix), the sky background, which is dominated by the diffuse galactic light as given in Fig. 42 of the FOC Instrument Handbook, and the contribution due to unresolved sources and to the wings of the PSF of the resolved sources. In order to estimate this third background component we take all the flux measured by Burstein et al. (1988, Ap.J. 328, 440) in the large IUE aperture and we assume it is distributed with a radial profile like the B-band one given by Kent (1987, A.J. 94, 306) for M32. In a 2 hour exposure with the F150W filter, subdivided into two single exposures slightly shifted by 1 arcsec, we foresee a S/N varying between 8 at the nucleus and 14 at the edge of the field for our reference PAGB star, while S/N will be 5 at 2 arcsec from the nucleus and 7 at the edge for a PAGB one magnitude fainter. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). VAX 730+1.5Gb disk+Jupiter 7 Image Disp/Decnetted to VAX 780 cluster at Dept. of Astronomy ASU. VAX 8530 + MIDAS/IRAF reduction packages in Padova. SUN IPC Workstations + MIDAS/IRAF packages in Firenze. ------------------------------------------------------------------------------------ 11. Address Information Name: FRANCESCO BERTOLA Category: PI Institution: Address: DIP.TO DI ASTRONOMIA VICOLO OSSERVATORIO, 5 City: PADOVA I-35122 State: Zip Code: Country: ITALY Telephone: Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 5722 [ 4] ------------------------------------------------------------------------------------------------------------------------------------ 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-UV- B, 131 PLATE-ID = 0738, 2000 V = -299 1 V=18.7+/-0.5, TYPE=O5 V, E(B- STARS M31 RA = 0H 42M 44.9S +/- 0.1S, 2 V)=0.08 DEC = +41D 16' 08" +/- 1" F(1500)=25+/-4E-18 Comments: FLUXVAL_2 IS FOR THE REFERENCE PAGB STAR AT 4" FROM THE NUCLEUS. ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5722 [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 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-UV- WFPC2 IMAGE PC1-FIX F160BW 1 50.0M 3 2 1 PCS MODE F / 1-3 STARS CYCLE 4 / 1-3 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC224-UV- WFPC2 IMAGE PC1-FIX F336W CR-SPLIT=0.5 1 7.7M 6 2 2 SAME ORIENT FOR 2- STARS CR- 3 AS 1 TOLERANCE=0.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC224-UV- WFPC2 IMAGE PC1-FIX F218W 1 26.7M 4 2 3 STARS ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5722 [ 6] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=0.5 CR-TOLERANCE=0.0 ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO/CAR ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 2.0 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR POPULATIONS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category OLD FIELD STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE F / 1-3; CYCLE 4 / 1-3 SAME ORIENT FOR 2-3 AS 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F160BW F336W F218W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC224-UV-STARS M31 ------------------------------------------------------------------------------------------------------------------------------------