8291( 11) - 03/12/01 14:08 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8291 Version: 11 Check-in Date: 12-Mar-2001 14:07:26 1.Proposal Title: The Alpha-Element/Iron Ratio in Starburst Populations ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Claus Leitherer Space Telescope Science Institute CoI: Dr. Alessandra Aloisi Universita di Bologna N CoI: Dr. Beatriz Barbuy Universidade de S\ ao Paulo N CoI: Dr. Mark Clampin Space Telescope Science Institute N CoI: Dr. Laura Greggio Universitaetssternwarte Muenchen N CoI: Dr. Antonella Nota Space Telescope Science Institute N CoI: Dr. Livia Origlia Osservatorio Astronomico di Bologna N CoI: Dr. Monica Tosi Osservatorio Astronomico di Bologna N CoI: Dr. Kim Venn Macalester College N ------------------------------------------------------------------------------------ 5. Abstract We propose STIS observations of A and F supergiants in NGC1569, the closest starburst galaxy. Spectra around 6200 Angstrom\ taken with the G750M grating will be used to determine element abundances of Fe and several Alpha-elements. The galaxy has experienced a strong starburst over the past few hundred Myr and possibly only very few and much less intense episodes of star formation at earlier epochs. Chemical evolution models predict a significant Alpha/Fe enhancement in the galaxy. This prediction is difficult --- if not impossible--- to verify from an abundance analysis of the gas phase. However, the issue can be settled with a direct abundance measurement in recently formed stars. The proposed STIS observations, in combination with the stellar atmosphere tools we have developed will allow such an abundance determination. These observations are the first abundance measurements of individual stars outside the Local Group. The determination of the Alpha/Fe ratio is fundamen tal to our understanding of the c h emical evolution history of this galaxy. It will also constrain the treatment of mixing processes in the hot and cold phase of the ISM and the enrichment of the intracluster and intergalactic medium. Ultimately, understanding local starbursts in detail will allow us to extrapolate to high redshift and to better understand galaxy evolution in the early universe. ------------------------------------------------------------------------------------ 8291( 11) - 03/12/01 14:08 - [ 2] Observations Description ------------------------ The target selection was performed with our existing multi- color WFPC2 images. Spectral types were derived from photometry after reddening correction. NGC1569 is at a Galactic latitude of only 11^degrees so that extinction is relatively large (E(B-V)=0.56). It is important to realize that almost all of the extinction is due to the foreground. Therefore a possibly variable intrinsic component is small. We restricted our sample to types A and F since these are the visually brightest supergiants and since our theoretical analysis is optimized for this temperature range. The Galaxy model of Bahcall & Soneira (1980) and number counts in adjacent control fields indicate that the expected number of Galactic foreground stars is negligible. Therefore all selected stars are supergiants in NGC1569. We excluded stars fainter than 20th magnitude for three reasons: first, because of S/N considerations, and second to bias the sample towards higher luminosities and therefore larger radii. Such stars have lower rotation vel ocity. Third, the brightest stars originate from the most massive stars and have the shortest lifetimes (<20 Myr for our sample). Crowding is severe, even with the spatial resolution of HST, and care in the target selection is required. Ground-based spectra would be heavily contaminated by nearby companions in this extreme starburst galaxy. We believe the minimum number of targets should be about five for a significant result. Taking advantage of the long-slit capabilities of STIS, we can obtain spectra of two stars in one exposure. Although we may achieve our goal with one exposure, we conservatively request three exposures (six stars). The most luminous stars sometimes exhibit instabilities with strong mass loss (so-called luminous blue variables). Our analysis tools do not allow us to derive abundances in such a star so that this spectrum would not be useful. Based on lifetime considerations we expect a few \ all luminous blue supergiants to be in this phase. This is sma l l but not entirely negligible. T h e six stars which were finally selected are in Table 1. Their positions in NGC1569 are indicated in Figure refimage, together with the planned slit positions and orientations. We will observe stars 1 and 2 with slit position 1. Fortuitously, star 4 will be inside the slit as well. We expect a somewhat degraded S/N for star 4 due to background from the nearby super star cluster and slight mis- centering. Therefore we will re-observe star 4 with star 3 in slit position 2. Our third slit position will cover stars 5 and 6. We need to emphasize that the proximity of star 4 to the super star cluster does not pose a contamination problem. The star is about 4 mag fainter than the cluster and the separation is 0.7''. The cluster PSF drops by more than three orders of magnitude between the cluster center and star 4. begintableh captionProgram stars. begincenter begintabularc c c c c c c c multicolumn1cStar & multicolumn1cx Pos & multicolumn1cy Pos & multicolumn1cV & multicolumn1c(B-V ) & multicolumn1cSp. Type& mult ico lumn1ct(G430L) & multicolumn1ct(G750M), multicolumn1c & multicolumn1c(pixel) & multicolumn1c(pixel) & multicolumn1cmag & multicolumn1cmag & multicolumn1c& multicolumn1c(s) & multicolumn1c(s), NGC1569- 1 & 289& 293& 19.57 & 0.73 & A5 I & 3600 & 26000 , NGC1569-2 & 314& 316& 19.51 & 0.82 & F0 I & 4100 & 22000 , NGC1569-3 & 366& 343& 18.34 & 0.87 & F2 I & 1400 & 6600 , NGC1569- 4 & 364& 359& 19.23 & 0.95 & F5 I & 4100 & 15000 , NGC1569-5 & 418& 392& 19.60 & 1.08 & F8 I & 7100 & 22000, NGC1569-6 & 433& 708& 19.52 & 0.74 & A7 I & 3300 & 23000 , endtabular endtable The target acquisition will be performed via an initial acquisition of the bright super star clusters in the center of NGC1569. The cluster was observed by us before with HST. It is almost a point source. Then an offset to the stellar targets will be done. We will use the standard 52x0.2 aperture for the science observations. At first, we will take a G430L spectrum for spectral cla ssification purposes. This wi l l al l ow us to derive T(eff)\ and \log g. Exposure times to reach S/N = 20 at 4300 Angstrom\ were calculated with the ETC. Typical values are around 4000 s (see Table 1). Next we observe with G750M for S/N = 35 at a central wavelength of 6252 Angstrom. This spectral region is well suited since numerous Alpha- element and Fe lines can be observed in one setting. We computed a model atmosphere grid to predict the expected strengths of the most important strategic lines and to define our spectral resolution and S/N requirements. Figure refspec is an example. The O I and Fe II lines will be resolved and can be analyzed at a resolving power of R = 10000 and S/N = 35. Lower S/N would make it difficult to measure weak lines and the abundance measurement would be compromised. The exposure times to reach S/N = 35 are in Table 1. Typical times are around 20000 s. NGC1569 can be observed in the CVZ, thereby significantly increasing the efficiency. The exposure times per slit position and or ientation are driven by th e fainte r of the two stars. The required exposure times are 26000 s + 4100 s = 30100 s, 15000 s + 4100 s = 19100 s, and 23000 s + 7100 s = 30100 s for positions 1, 2, and 3, respectively. One CVZ orbit gives 5700 s of time. Accounting for instrumental overhead, we require 7, 4, and 7 orbits per stellar pair. The 7 orbit visits will be split into 3 and 4 orbit visits. The additional overhead has already been accounted for. Therefore we ask for a total of 18 orbits. Real Time Justification ----------------------- We request that the observations be scheduled in the CVZ. The galaxy is ideally suited for CVZ observations and was observed by us before during CVZ. Since we require a specific orientation, we need to verify that there are scheduling windows for the CVZ and ORIENT special requirements combined. We processed a phase2 template with our requirements using RPS2 and found at least 2 multi- orbit windows during Cycle 8. SAA impact could not be studied but is unlikely to be a problem since only 4 contiguous orbits are requested. We note that our Cycle 6 WFPC2 observations of NGC1569 had the CVZ and ORIENT requirements as well, causing no scheduling problems. No supporting/coordinated observations that would affect scheduling are planned. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8291( 11) - 03/12/01 14:08 - [ 3] Data Distribution Paper Products: Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8291( 11) - 03/12/01 14:08 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC1569-A EXT-CLUSTER, GLOBULAR RA=4H 26M 3.7S +/- 0.1S, DEC=64D 1950 V = 14.9 CLUSTER 44' 29.0" +/- 1" V-I = 1.0 Coordinate Source: Comments: Cluster used for target acquisition 10 NGC1569-1-2 EXT-STAR, A4-A9 III-I, RA-OFF=-0.5885S+/- 0.01S, DEC- 1950 V = 19.5 F0-F2, F3-F9 OFF=2.926"+/- 0.1", FROM 1 B-V = 0.8 20 NGC1569-3-4 EXT-STAR, A4-A9 III-I, RA-OFF=0.0133S+/- 0.01S, DEC- 1950 V = 19.5 F0-F2, F3-F9 OFF=1.334"+/- 0.1", FROM 1 B-V = 0.8 30 NGC1569-5-6 EXT-STAR, A4-A9 III-I, RA-OFF=0.4406S+/- 0.01S, DEC- 1950 V = 19.5 F0-F2, F3-F9 OFF=-0.449"+/- 0.1", FROM 1 B-V = 0.8 40 NGC1569-6 EXT-STAR, A4-A9 III-I RA=4H 30M 49.14S+/- 0.01S, J2000 V = 19.5 DEC=64D 50' 43.9"+/-0.1", PLATE- B-V = 0.8 ID=01MS 8291( 11) - 03/12/01 14:08 - [ 5] Visit: 01 Visit Priority: Visit Requirements: CVZ ORIENT 165.76D TO 165.96D ORIENT 345.76D TO 345.96D On Hold Comments: Additional Comments: Orientation + 180 D ok as well Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC1569-A STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 2 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 15 NGC1569-1-2 STIS/C ACQ/PEA 52X0.2 MIRROR 1 30 S CD K ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC1569-1-2 STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=3 1 4800 S CD ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC1569-1-2 STIS/C ACCUM 52X0.2 G750M 6252 CR-SPLIT=6 1 15504 S CD ------------------------------------------------------------------------------------------------------------------------------------ 8291( 11) - 03/12/01 14:08 - [ 6] Visit: 02 Visit Priority: Visit Requirements: CVZ ORIENT 165.76D TO 165.96D ORIENT 345.76D TO 345.96D On Hold Comments: Additional Comments: Orientation + 180 D ok as well Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC1569-A STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 2 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC1569-1-2 STIS/C ACQ/PEA 52X0.2 MIRROR 1 30 S CD K ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC1569-1-2 STIS/C ACCUM 52X0.2 G750M 6252 CR-SPLIT=6 1 15000 S CD ------------------------------------------------------------------------------------------------------------------------------------ 8291( 11) - 03/12/01 14:08 - [ 7] Visit: 03 Visit Priority: Visit Requirements: CVZ ORIENT 221.84D TO 222.04D ORIENT 41.84D TO 42.04D On Hold Comments: Additional Comments: Orientation + 180 D ok as well Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC1569-A STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 2 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 15 NGC1569-3-4 STIS/C ACQ/PEA 52X0.2 MIRROR 1 30 S CD K ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC1569-3-4 STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=3 1 4800 S CD ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC1569-3-4 STIS/C ACCUM 52X0.2 G750M 6252 CR-SPLIT=6 1 15570 S CD ------------------------------------------------------------------------------------------------------------------------------------ 8291( 11) - 03/12/01 14:08 - [ 8] Visit: 04 Visit Priority: Visit Requirements: CVZ ORIENT 31.91D TO 32.11D ORIENT 211.91D TO 212.11D On Hold Comments: Additional Comments: Orientation + 180 D ok as well Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC1569-A STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 2 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 15 NGC1569-5-6 STIS/C ACQ/PEA 52X0.2 MIRROR 1 30 S CD K ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC1569-5-6 STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=3 1 8700 S CD ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC1569-5-6 STIS/C ACCUM 52X0.2 G750M 6252 CR-SPLIT=6 1 11754 S CD ------------------------------------------------------------------------------------------------------------------------------------ 8291( 11) - 03/12/01 14:08 - [ 9] Visit: 05 Visit Priority: Visit Requirements: CVZ ORIENT 31.91D TO 32.11D ORIENT 211.91D TO 212.11D On Hold Comments: Additional Comments: Orientation + 180 D ok as well Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC1569-A STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 2 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC1569-5-6 STIS/C ACQ/PEA 52X0.2 MIRROR 1 30 S CD K ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC1569-5-6 STIS/C ACCUM 52X0.2 G750M 6252 CR-SPLIT=6 1 15000 S POS TARG 0.0, 7.0 CD ------------------------------------------------------------------------------------------------------------------------------------ 8291( 11) - 03/12/01 14:08 - [ 10] Visit: 54 Visit Priority: Visit Requirements: CVZ On Hold Comments: Additional Comments: Orientation + 180 D ok as well (orient removed for HOPR) Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC1569-6 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 60 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC1569-6 STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=3 1 8900 S CD ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC1569-6 STIS/C ACCUM 52X0.2 G750M 6252 CR-SPLIT=6 1 11754 S CD ------------------------------------------------------------------------------------------------------------------------------------ 8291( 11) - 03/12/01 14:08 - [ 11] Visit: 55 Visit Priority: Visit Requirements: CVZ On Hold Comments: Additional Comments: Orientation + 180 D ok as well. Orient removed for HOPR. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC1569-6 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 60 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC1569-6 STIS/C ACCUM 52X0.2 G750M 6252 CR-SPLIT=6 1 15200 S CD ------------------------------------------------------------------------------------------------------------------------------------ 8291( 11) - 03/12/01 14:08 - [ 12] Summary Form for Proposal 8291 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT CR-SPLIT=3 CR-SPLIT=6 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ ORIENT 165.76D TO 165.96D ORIENT 345.76D TO 345.96D CVZ ORIENT 221.84D TO 222.04D ORIENT 41.84D TO 42.04D CVZ ORIENT 31.91D TO 32.11D ORIENT 211.91D TO 212.11D POS TARG 0.0, 7.0 CVZ ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G430L G750M ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC1569-A NGC1569-1-2 NGC1569-3-4 NGC1569-5-6 NGC1569-6 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 4300 6252 ------------------------------------------------------------------------------------------------------------------------------------