! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6445,v 6.1 1996/08/22 17:49:37 pepsa Exp $ ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6445,v 6.1 1996/08/22 17:49:37 pepsa Exp $ ! ! Refer to the HST Phase II Proposal Instructions to fill this out ! ! Anything after a "!" is ignored, and may be deleted ! ! All keywords with multiple entries are comma delimited except the ! Visit_Requirements and Special_Requirements keywords which can be ! delimited with carriage returns or semi-colons, but not commas ! ! For help call your Program Coordinator: Manning ! Phone: 410-338-4456 , E-mail: manning@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. ! Name of Phase I Proposal: archive-0159.simon.prop ! Date generated: Fri Dec 22 16:44:41 EST 1995 ! Proposal_Information ! Section 4 Title: A Hyades Enigma: 71 Tauri Proposal_Category: GO Scientific_Category: COOL STARS Cycle: 6 Investigators PI_name: Theodore Simon PI_Institution: University of Hawaii Abstract: ! Free format text (please update) 71 Tau is the second most powerful X-ray source in the Hyades Cluster, yet its UV chromospheric emission lines appear comparatively weak in low dispersion IUE spectra. 71 Tau shows puzzling photometric changes in the UV, varying in brightness on at least one occasion by as much as 30\% in IUE spectra near 1800--2000 Angstrom. Its behavior suggests a possible, new mode of A--F star variability. There is some evidence to suggest that many other A and F stars may behave the same way, fluctuating by small amounts in UV brightness and changing their effective temperatures by no more than 50- -100 K. Relying on the greater sensitivity and inherent stability of the GHRS, we propose to use this instrument to obtain a spectroscopic light curve of 71 Tau over the 1200-- 1900 Angstrom\ region. From this time series of GHRS spectra, we will try to demonstrate whether and in what manner the UV brightness of 71 Tau varies, in order to determine whether such brightness changes can be reconciled with radial or non- radial pulsations of the star. Questions ! Free format text (please update) Observing_Description: noindent GOALS. We request time to observe a spectroscopic light curve of 71 Tau, using the GHRS to obtain a time series of spectra from which the light variations of this star can be followed at wavelengths ranging from 1200Angstrom\ to 1900Angstrom. With these observations we seek to determine (1) whether the UV luminosity of 71 Tau varies, (2) if the star does vary, whether the changes are consistent with a small, 10\% amplitude and 3.9--hour timescale expected for \dsct\ pulsations, (3) whether there are any larger flux changes, possibly as great as 30\% (which may have an origin in a new mode of F star variability), (4) whether the UV brightness changes are attributable to 50--100 K variations in T_ eff andor by changes in the radius and surface gravity of the star (NB: it is possible to learn this only from the UV, by fitting model atmosphere fluxes over a broad wavelength range, and it cannot be done from optical photometry alone), (5) whether the chromospheric line emission in C II is truly as weak (and possibly as variable) as low S/N observations from IUE now indicate, (6) whether we can find evidence for chromospheric emission in the higher temperature Si IV lines, which may give us some insight into the powerful X-ray emission of 71 Tau, but which have not been detected before in IUE spectra of this star (the absence of both C II and Si IV would argue that the observed X-ray emission comes not from the F star but from a hidden companion star), and (6) whether the strengths of the UV emission lines are modulated with the UV continuum, or whether they remain steady even as the continuum varies (the existing, contradictory evidence on this from IUE has implications for the source of chromospheric heating in the A --F stars: see Ayres 1991 ApJ 375, 704)., noindent CONFIGURATION. The observations of 71 Tau will be made with the D1 detector, the G140L grating, and the large science aperture of the GHRS. For high S/N, we plan to use the normal ACCUM mode in order to take advantage of certain capabilities of the exposure control software (e.g., substepping) that would be deactivated in the alternative RAPID mode. Two separate exposures, at different settings of the grating carrousel, will be required to observe the entire short wavelength spectrum, one centered on 1750Angstrom\ to cover the bright continuum from 1600Angstrom\ to 1900Angstrom, and the other centered on 1425Angstrom\ to cover the fainter short wavelength continuum and chromospheric emission lines of C II and Si IV in the 1275- -1575Angstrom\ region., noindent COUNT RATES. To estimate flux levels and count rates over the full wavelength range, we have used existing IUE spectra of 71 Tau. The appropriate sensitivities were taken from Table 8--2 of the GHRS Instrument Handbook. At two representative wavelengths, 1300Angstrom\ and 1800Angstrom, our flux and count rate estimates are: at 1300Angstrom, 9 * 10^-14 \ergcm2sa\ for the flux and 1.5 ct s^-1, respectively; and at 1800Angstrom, 1.5 * 10^-11 \ergcm2sa\ and 15.8 cts s^-1, respectively. For these count rates, exposure times of 326.4 seconds in the short wavelength region and 108.8 seconds in the long wavelength region are expected to give a S/N ratio of greater than 25:1 per diode across the entire wavelength range from 1275Angstrom\ to just longward of 1850 Angstrom dropping to 13:1 at 1900Angstrom\ as the sensitivity of the camera falls off. Photometry in wider spectral bands, i.e., averaging over several diodes, should provide correspondingly higher S/N ratios for detecting very small continuum brightness changes., noindent FEASIBILITY. We have used the RPS2 software to carry out a feasibility check of an observing program comprised of a total of 3 orbits, which would cover an entire 3.9-hour \dsct\ pulsation cycle. We propose to alternate between 108^s exposures of the 1600--1900Angstrom\ region and 326^s exposures of the 1275--1575Angstrom\ region. Switching between grating positions in this way entails an overhead of ~160^s for each exposure. We could avoid this inefficiency by taking a sequence of exposures at a fixed grating setting. However, our objective here is to cover the whole 1200--1900Angstrom\ wavelength range at once --- so that we can match each spectrum to a model atmosphere flux distribution over as wide a wavelength range as possible in order to infer estimates of T_ eff and log g --- and therefore the short-- and long--wavelength regions need to be observed in quick succession. (To observe the same 1200-- 1900Angstrom\ wavelength range with STIS will involve a comparable amount of overhead.) According to the RPS2 software, it should be possible to fit a total of 22 spectra, 11 at each grating setting, within the allocation of 3 HST orbits we are requesting for this program: 3 pairs of spectra in the first orbit, 4 pairs in the second orbit, and 4 pairs in the third orbit. We have used the timing of the individual spectra from the RPS2 output to see whether or not photometric variability could be detected for the proposed set of observations. We assumed a sinusoidal variation having an amplitude of 10\%. According to Section 2.1.3 of the GHRS users' manual, the repeatability of large aperture flux measurements with the GHRS, at a given wavelength, is 1\%. Assuming a more conservative error of 2\% per data point, we found a minimum reduced chi^2_Nu = 8 for 10 d.o.f. for our simulated data set, depending on the phasing of the observations with respect to the light curve. Generally these values were larger. Detecting even small amplitude UV light variability should therefore not be a problem, especially if the variations turn out to be as large as 30\%. Real_Time_Justification: None. We are exploring arrangements for getting optical time series photometry of 71 Tau, which might help to clarify the behavior and nature of its light variations at visible wavelengths. Calibration_Justification: Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: HD28052 Alternate_Names: 71-TAU Description: STAR, F0-F2 Position: ! HIC 20713 RA=04H 26M 20.8S +/- 0.3", DEC=+15D 37' 06.1" +/- 0.3" ! PLATE-ID=0000 Equinox: 2000 RV_or_Z: V = 38.3 RA_PM: +0.0077 Dec_PM: -0.024 Epoch: 2000 Annual_Parallax: 0.022 Flux: V = 4.50 +/- 0.02, B-V = 0.26 +/- 0.02 Comments: Visits ! Section 6 Visit_Number: 1 Visit_Requirements: SEQ 1-2 WITHIN 1H ! Section 7.1 On_Hold_Comments: Visit_Comments: Do visits 1+2 sequentially, no time gap. Exposure_Number: 100 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACQ Aperture: 2.0 Sp_Element: MIRROR-N1 Wavelength: Optional_Parameters: SEARCH-SIZE = 3, BRIGHT = RETURN ! STEP-TIME = 0.6 ! EXPECT 4000 COUNTS IN STEP-TIME Number_of_Iterations: 1 Time_Per_Exposure: 5.4S Special_Requirements: ONBOARD ACQ FOR 101-113 ! Section 7.2 Comments: Exposure_Number: 101 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1750 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 108.8S Special_Requirements: ! Section 7.2 Exposure_Number: 102 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1425 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 326.4S Special_Requirements: ! Section 7.2 Comments: Exposure_Number: 103 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1750 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 108.8S Special_Requirements: ! Section 7.2 Exposure_Number: 104 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1425 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 326.4S Special_Requirements: ! Section 7.2 Comments: Exposure_Number: 105 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1750 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 108.8S Special_Requirements: ! Section 7.2 Exposure_Number: 106 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1750 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 108.8S Special_Requirements: ! Section 7.2 Exposure_Number: 107 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1750 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 108.8S Special_Requirements: ! Section 7.2 Exposure_Number: 108 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1425 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 326.4S Special_Requirements: ! Section 7.2 Comments: Exposure_Number: 109 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1750 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 108.8S Special_Requirements: ! Section 7.2 Exposure_Number: 110 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1425 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 326.4S Special_Requirements: ! Section 7.2 Comments: Exposure_Number: 111 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1750 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 108.8S Special_Requirements: ! Section 7.2 Exposure_Number: 112 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1425 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 435.2S Special_Requirements: ! Section 7.2 Comments: Exposure_Number: 113 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1750 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 108.8S Special_Requirements: ! Section 7.2 Visit_Number: 2 Visit_Requirements: ! Section 7.1 On_Hold_Comments: Visit_Comments: Exposure_Number: 200 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACQ Aperture: 2.0 Sp_Element: MIRROR-N1 Wavelength: Optional_Parameters: SEARCH-SIZE = 3, BRIGHT = RETURN ! STEP-TIME = 0.6 ! EXPECT 4000 COUNTS IN STEP-TIME Number_of_Iterations: 1 Time_Per_Exposure: 5.4S Special_Requirements: ONBOARD ACQ FOR 201-205 ! Section 7.2 Comments: Exposure_Number: 201 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1750 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 108.8S Special_Requirements: ! Section 7.2 Comments: Exposure_Number: 202 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1425 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 326.4S Special_Requirements: ! Section 7.2 Comments: Exposure_Number: 203 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1750 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 108.8S Special_Requirements: ! Section 7.2 Exposure_Number: 204 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1425 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 326.4S Special_Requirements: ! Section 7.2 Comments: Exposure_Number: 205 ! Section 6.5 Target_Name: HD28052 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1750 Optional_Parameters: FP-SPLIT = STD, DOPPLER = ON, STEP-PATT = 5 Number_of_Iterations: 1 Time_Per_Exposure: 108.8S Special_Requirements: ! Section 7.2 Data_Distribution ! Defaults indicated; change if desired Medium: 8MM ! 8MM or 6250BPI or 1600BPI Blocking_Factor: 10 ! 10 or 1 ! Only astronomers with very old 9- ! track tape drives should consider ! a blocking factor of 1 Ship_To: PI_Address ! STSCI or PI_Address or <free-text> ! PI Address from Phase I is: ! ! Institute for Astronomy ! 2680 Woodlawn Drive ! Honolulu ! 96822 ! ! Ship_Via: UPS ! UPS (2-day) or OVERNIGHT ! Overnight shipping done at PI expense Recipient_Email: ! Needed if Ship_To: is not PI_Address ! <free-text> ! Let us know what you think of this template and software! ! Please send a list of your likes and dislikes to your Program Coordinator