! $Id: 6709,v 6.1 1996/07/26 18:12:39 pepsa Exp $ Proposal_Information Title: Heavy Element Abundances in AV 304, a B0.5 Main Sequence Star in the Small Magellanic Cloud Proposal_Category: GO Scientific_Category: HOT STARS Cycle: 6 Investigators PI_name: Geraldine Peters PI_Institution: University of Southern California CoI_Name: James Grigsby CoI_Institution: Wittenberg University Contact: N ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) We propose HST/GHRS of AV 304, a sharp-lined B0.5 main sequence star in the Small Magellanic Cloud, to determine the abundances of heavy elements, especially those of the iron group. For this exploratory study, we have selected three spectral fields (using the G160M grating) that contain measurable features of Ti III, V III, Cr III, Mn III, and Fe III, as well as prominent lines of C III, Si II, III, and S II. An analysis of ground-based data of this 15th magnitude star by Dufton, et al. (1990) revealed an average underabundance of 0.7 dex for most light elements, but a normal He abundance. This will be the first attempt to measure the abundances of Fe group elements in the photosphere of an early B, main sequence star in an external galaxy. Although abundances of the Fe-peak elements are of interest because they are important for assessing opacities for stellar evolution calculations and the validity of theoretical calculations of explosive nucleosynthesis, the above-mentioned study did not yield this information because measurable lines from these species are found only in the UV spectral region. Abundances and abundance ratios of both heavy & light elements will be compared with results from H II regions, supernova remnants, and evolved massive stars in the SMC and theoretical calculations of nucleosynthesis. Questions ! Free format text (please update) Observing_Description: For this project we are targeting three spectral fields that contain a large number of relatively strong lines from the Fe group elements. We have decided to used grating G160M which will give us a resolution of about 0.07 Angstrom and a bandpass of 35 Angstrom. Further details, including exposure times & important ions contained in the bandpass, are provided in Table 1. TABLE 1 Ion Species Contained in Proposed Spectral Fields Sp. Interval Exposure Time Species Contained in Field 1235-1270 90 min. Si II (UV4), S II (UV 1 & 2), V III (UV 7), Cr III (UV 21) 1280-1315 70 min. Si III (UV 4), Ti III(UV1&2), Mn III (UV 9) 1880-1915 180 min. Fe III (UV 34, 52, 53, 83, 96) We propose that target acquisition be done in the LSA using the mirror-N2. This will prevent a side-switch (and 40 min. overhead) in order to use the grating G160M. Since AV 304 has a very small reddening (E(B - V=0.08), we predict a sufficiently high count rate of about 3,000 counts with N2. We will obtain all three spectral fields with the LSA. Exposure times were determined using Case 1 (p. 33) in the GHRS Instrument Handbook, the known V magnitude and E(B-V) of the star, and a Kurucz model of T_eff=28,000 K/ log g = 4.0 (Dufton, et al. 1990) for a desired S/N or 25 for the two fields near 1275 Angstrom and 15 for the 1900 Angstrom exposure. Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: AV304 Alternate_Names: Description: EXT-STAR, B0-B2 V-IV Position: RA=1H 02M 21.44S +/- 0.1S, DEC=-72D 39' 14.59" +/- 0.50", PLATE-ID=06B1 Equinox: J2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux: V = 14.98 B-V = -0.20 U-B = -0.98 E(B-V) = 0.08 F-CONT(1300)=1.9e-13 Comments: Visits ! Section 6 Visit_Number: 01 Visit_Requirements: ! Section 7.1 On_Hold_Comments: Visit_Comments: Exposure_Number: 10 ! Section 6.5 Target_Name: AV304 Config: HRS Opmode: ACQ Aperture: 2.0 Sp_Element: MIRROR-N2 Wavelength: Optional_Parameters: BRIGHT=RETURN,SEARCH-SIZE=3 Number_of_Iterations: 1 Time_Per_Exposure: 4.5S Special_Requirements: ONBOARD ACQ FOR 20-50 Exposure_Number: 20 Target_Name: AV304 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G160M Wavelength: 1252.5 Optional_Parameters: SPYBAL=YES,FP-SPLIT=NO Number_of_Iterations: 18 Time_Per_Exposure: 299.2S Special_Requirements: Comments: Exposure_Number: 30 Target_Name: AV304 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G160M Wavelength: 1297.5 Optional_Parameters: SPYBAL=YES,FP-SPLIT=NO Number_of_Iterations: 14 Time_Per_Exposure: 299.2S Special_Requirements: Comments: Exposure_Number: 40 Target_Name: AV304 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G160M Wavelength: 1892.5 Optional_Parameters: SPYBAL=YES,FP-SPLIT=NO Number_of_Iterations: 18 Time_Per_Exposure: 299.2S Special_Requirements: Comments: Exposure_Number: 50 Target_Name: AV304 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G160M Wavelength: 1892.5 Optional_Parameters: SPYBAL=YES,FP-SPLIT=NO Number_of_Iterations: 18 Time_Per_Exposure: 299.2S Special_Requirements: Comments: Data_Distribution Medium: 8MM Blocking_Factor: 10 Ship_To: PI_Address Ship_Via: UPS Recipient_Email: