10773(  3) - 11/15/05 09:35  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10773

Version: 3    Check-in Time: 15-Nov-2005 14:34:33

Title
Calibrating the Mass-Luminosity Relation at the End of the Main Sequence
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Type             Cycle     Parallel Pointing Tolerance
GO               13        <none>
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Investigators
                                                                                     Contact?
    PI: Dr. Todd J. Henry                 Georgia State University Research
                                          Foundation
   CoI: Dr. George Fritz Benedict         University of Texas at Austin                 N
   CoI: Dr. Otto Franz                    Lowell Observatory                            N
   CoI: Dr. Philip A. Ianna               The University of Virginia                    N
   CoI: Dr. Barbara McArthur              University of Texas at Austin                 N
   CoI: Dr. Edmund Nelan                  Space Telescope Science Institute             N
   CoI: Dr. Lawrence H. Wasserman         Lowell Observatory                            N

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Abstract

We propose to use HST-FGS1R to calibrate the mass-luminosity relation (MLR) for
stars less massive than 0.2 Msun, with special emphasis on objects near the
stellar/brown dwarf border. Our goals are to determine M_V values to 0.05 magnitude,
masses to 5\ than double the number of objects with masses determined to be less
than 0.20 Msun. This program uses the combination of HST-FGS3/FGS1R at optical
wavelengths and ground-based infrared interferometry to examine nearby, subarcsecond
binary systems. The high precision measurements with HST-FGS3/FGS1R (to 1 mas in the
separations) for these faint targets (V = 10--15) simply cannot be equaled by any
ground based technique. As a result of these measurements, we are deriving high
quality luminosities and masses for the components in the observed systems, and
characterizing their spectral energy distributions from 0.5 to 2.2 Mum. Several of
the objects included have M < 0.1 Msun, placing them at the very end of the stellar
main sequence. Three of the targets are brown dwarf candidates, including the
current low mass record holder, GJ 1245C, with a mass of 0.062 +/- 0.004 Msun. The
payoff of this proposal is high because all 10 of the systems selected have already
been resolved with HST- FGS3/FGS1R during Cycles 5--10 and contain most of the
reddest objects for which masses can be determined.
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                                                10773(  3) - 11/15/05 09:35  - [  2]

  Observations Description
  ------------------------

     Cycle 5--13 Update: FGS-TRANS observations of the systems were (generally) made
     at the beginning and end of Cycle 5 and once each in Cycles
     6/7/8/9/10/11/12/13, resulting in about six observations so far for each system
     (except Gl 54 and GJ 2005, which were added more recently). Additional Cycle 10
     measurements have not yet been carried out for eight of the systems. The TRANS
     mode observations are used to map the binary orbits via determination of the
     separations and position angles, and to measure the magnitude difference of the
     components so that luminosities can be derived. In Cycles 8-13 FGS-POS
     measurements have been made to locate the position of the center of mass of
     each system with respect to background stars. This allows us to determine the
     fractional masses of the components so that individual masses can be derived.
     Because of the long orbital periods of these systems, radial velocity
     techniques are not typically useful in getting fractional masses because the
     velocity differences are small, in addition to the complicating factor that the
     systems are generally faint and the velocities are of poor precision. The
     timing of observations has been carefully planned to provide points on the
     orbits every 20--30^degrees, and a similar strategy will be used in Cycles
     11/12/13. Experience from Gl 748 (17 observations) and Gl 791.2 (14
     observations) indicates that a set of roughly 12 measurements spread around the
     orbit is sufficient to achieve orbital parameter errors smaller than 1\ error
     in the semimajor axis triples in Kepler's Third Law, which is why we need
     orbital elements with minimal error, and the consequent orbital coverage. Cycle
     11--13 Plan: We propose to continue this effort to (1) increase the orbital
     coverage from six to nine years, thereby passing the critical half-orbit point
     on all of the systems, (2) determine the first masses for six systems, (3)
     revise masses for four systems, (4) refine the brightness ratios, and (5)
     employ the low-cost (in the sense of number of orbits) technique to measure the
     fractional masses in nine systems. In essence, via this program HST-FGS will be
     the instrument responsible for defining the MLR for the most populous stars in
     the Galaxy --- not a bad legacy for the sometimes forgotten HST instrument.
     Each of the 10 systems will be observed once each Cycle in FGS-TRANS mode
     through filter F583W to determine the separation, position angle, and
     brightness difference between the components. For the TRANS mode observations,
     20--60 scans 0.8--3.0" in length are typically made across the binary. The
     F583Waperture has been selected because it is the best calibrated of the
     filters available in FGS. The transmission of the telescope through F583W is
     already calibrated to the Johnson V band (Henry et al 1999), and will allow the
     magnitude difference at visible wavelengths to be attained with high accuracy.
     During the same orbit, nine of the systems will be observed in FGS-POS mode to
     relate the binary to a background grid of stars in order to find the center of
     mass (Gl 473 is the lone exception because it lacks reference stars). POS mode
     observations will include multiple runs through the field. The POS mode
     observations allow to get fractional masses for each system. Over time, the
     vector connecting the two components rotates about the center of mass as they
     orbit one another. By overlapping the yearly vectors, we pinpoint the center of
     mass and derive the fractional masses, provided that the movement of the system
     due to its proper motion and parallax can be removed using accurate ground-
     based data. Errors in the location of vector overlap due to parallax
     uncertainties are minimized by observing the systems at nearly the same time
     every year. GJ 1215 and GJ 2005 are the most difficult targets due to
                                                10773(  3) - 11/15/05 09:35  - [  3]

     faintness, but they are arguably the most important targets --- their
     secondaries have masses in the brown dwarf regime.

  Real Time Justification
  -----------------------


  Calibration Justification
  -------------------------


  Additional Comments
  -------------------

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                                                10773(  3) - 11/15/05 09:35  - [  4]

TARGET LIST    Fixed Targets
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Tar|   Target   |         Target        |            Target              |Coord   | Radial |             Flux data
No |    Name    |       Description     |           Position             |Eqnx    |  Vel.  |
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10  GL22         STAR, M V-IV            RA=00H32M24.7000S +/- 0.01S,     J2000             V = 10.38+/-0.05
                                         DEC=+67D14'11.90" +/- 0.2"
    Coordinate Source: GUIDE_STAR_CATALOG
    Comments: B-V = 1.54+/-0.05 TYPE=M2V BEWARE: second component at
              4" with V = 12.4

   Epoch of Position    RA proper motion (seconds of time/yr)    DEC Proper Motion (arcsec/yr)    Annual Parallax (arcsec)
   1983.84              0.29504                                  -0.2372                          0.09809

11  GL22-024-REF CALIBRATION,            RA=00H32M18.3840S +/- 1",        J2000             V = 12.6+/-0.2
                 ASTROMETRIC             DEC=+67D13'7.03" +/- 1"
    Coordinate Source: GUIDE_STAR_CATALOG

12  GL22-049-REF CALIBRATION,            RA=00H32M22.1780S +/- 1",        J2000             V = 13.3+/-0.2
                 ASTROMETRIC             DEC=+67D11'55.21" +/- 1"
    Coordinate Source: GUIDE_STAR_CATALOG

13  GL22-087-REF CALIBRATION,            RA=00H32M12.7900S +/- 1",        J2000             V = 13.4+/-0.2
                 ASTROMETRIC             DEC=+67D13'19.92" +/- 1"
    Coordinate Source: GUIDE_STAR_CATALOG

14  GL22-129-REF CALIBRATION,            RA=00H32M10.2790S +/- 1",        J2000             V = 11.2+/-0.2
                 ASTROMETRIC             DEC=+67D19'21.29" +/- 1"
    Coordinate Source: GUIDE_STAR_CATALOG

15  GL22-142-REF CALIBRATION,            RA=00H31M57.9170S +/- 1",        J2000             V = 13.6+/-0.2
                 ASTROMETRIC             DEC=+67D17'7.40" +/- 1"
    Coordinate Source: GUIDE_STAR_CATALOG

                                                10773(  3) - 11/15/05 09:35  - [  5]

Visit: 01
     Visit Priority:      <none>
     Visit Requirements:  SCHED 70%; ORIENT 73.0D TO 90.0 D; BETWEEN 12-DEC-2005:00:00:00 AND 29-DEC-
                          2005:00:00:00
     On Hold Comments:    <none>
     Additional Comments: scanlength 1.5"


Exposures
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Exp |   Target  | Instr  | Oper. | Aper    |Spectral|Central|           Optional           |Num|   Time   |       Special
Num |    Name   | Config | Mode  | or FOV  |Element |Waveln.|          Parameters          |Exp|          |     Requirements
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1    GL22        FGS      TRANS   1         F583W            STEP-SIZE=1,SCANS=12           1   950 S      POS TARG 0, 35; SEQ 1-15
                                                                                                           NON-INT
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2    GL22        FGS      POS     1         F583W                                           1   20 S       SAME POS AS 1
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3    GL22-024-RE FGS      POS     1         F583W                                           1   20 S       SAME POS AS 1
     F
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4    GL22-087-RE FGS      POS     1         F583W                                           1   20 S       SAME POS AS 1
     F
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5    GL22-024-RE FGS      POS     1         F583W                                           1   20 S       SAME POS AS 1
     F
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6    GL22-049-RE FGS      POS     1         F583W                                           1   20 S       SAME POS AS 1
     F
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7    GL22        FGS      POS     1         F583W                                           1   20 S       SAME POS AS 1
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8    GL22-024-RE FGS      POS     1         F583W                                           1   20 S       SAME POS AS 1
     F
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9    GL22-087-RE FGS      POS     1         F583W                                           1   20 S       SAME POS AS 1
     F
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10   GL22-049-RE FGS      POS     1         F583W                                           1   20 S       SAME POS AS 1
     F
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11   GL22-087-RE FGS      POS     1         F583W                                           1   20 S       SAME POS AS 1
     F
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12   GL22-024-RE FGS      POS     1         F583W                                           1   20 S       SAME POS AS 1
     F
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13   GL22        FGS      POS     1         F583W                                           1   20 S       SAME POS AS 1
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14   GL22-049-RE FGS      POS     1         F583W                                           1   20 S       SAME POS AS 1
     F
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                                                10773(  3) - 11/15/05 09:35  - [  6]

Exposures
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Exp |   Target  | Instr  | Oper. | Aper    |Spectral|Central|           Optional           |Num|   Time   |      Special
Num |    Name   | Config | Mode  | or FOV  |Element |Waveln.|          Parameters          |Exp|          |     Requirements
-----------------------------------------------------------------------------------------------------------------------------------
15   GL22-087-RE FGS      POS     1         F583W                                           1   20 S       SAME POS AS 1
     F
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Sub Exposures
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Target             | Exp |Instr   | Oper. |  Aper  |Spectral|Cent.|Primary     |Secondary   |Iteration |CR-SPLIT  |Orbit  |Duration
Name               | Num |Config  | Mode  | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num       |Num       |Number |
------------------------------------------------------------------------------------------------------------------------------------
GL22                1     FGS      TRANS   1        F583W          none         none         none       none       1       N/A
GL22                2     FGS      POS     1        F583W          none         none         none       none       1       N/A
GL22-024-REF        3     FGS      POS     1        F583W          none         none         none       none       1       N/A
GL22-087-REF        4     FGS      POS     1        F583W          none         none         none       none       1       N/A
GL22-024-REF        5     FGS      POS     1        F583W          none         none         none       none       1       N/A
GL22-049-REF        6     FGS      POS     1        F583W          none         none         none       none       1       N/A
GL22                7     FGS      POS     1        F583W          none         none         none       none       1       N/A
GL22-024-REF        8     FGS      POS     1        F583W          none         none         none       none       1       N/A
GL22-087-REF        9     FGS      POS     1        F583W          none         none         none       none       1       N/A
GL22-049-REF        10    FGS      POS     1        F583W          none         none         none       none       1       N/A
GL22-087-REF        11    FGS      POS     1        F583W          none         none         none       none       1       N/A
GL22-024-REF        12    FGS      POS     1        F583W          none         none         none       none       1       N/A
GL22                13    FGS      POS     1        F583W          none         none         none       none       1       N/A
GL22-049-REF        14    FGS      POS     1        F583W          none         none         none       none       1       N/A
GL22-087-REF        15    FGS      POS     1        F583W          none         none         none       none       1       N/A
                                                10773(  3) - 11/15/05 09:35  - [  7]

            Summary Form for Proposal  10773

  Item                         Used in this proposal
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  Apertures                    1
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  Configurations               FGS
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  Opmodes                      TRANS POS
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  Optional Parameters          STEP-SIZE=1 SCANS=12
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  Special Requirements         SCHED 70%; ORIENT 73.0D TO 90.0 D; BETWEEN 12-DEC-2005 00 00 00 AND 29-DEC-2005 00 00 00; POS TARG
                               0, 35; SEQ 1-15 NON-INT; SAME POS AS 1;
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  Spectral Elements            F583W
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  Target Names                 GL22 GL22-024-REF GL22-087-REF GL22-049-REF
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