! 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>

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