Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5355 Report Date: 18-Jul-95:17:13 Version: ********** Check-in Date: ********** 1.Proposal Title: THE BINARY FREQUENCY AMONG SOLAR-TYPE STARS IN YOUNG CLUSTERS: CYCLE4 HIGH ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID COOL STARS GO Sub Category EARLY EVOLUTION ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Stephen E. Strom 2001 USA 413-545-2290 ------------------------------------------------------------------------------------ 7. Abstract Recent ground-based observations have led to the unexpected conclusion that most and possibly all of the youngest, optically-visible solar-type pre-main sequence stars are members of binary or multiple star systems. However, this result is based solely on examination of stars located in sparsely populated, nearby star-forming complexes (e.g. Taurus) which are not representative of those that produce most of the stars which populate the Milky Way: giant molecular clouds (GMCs) which give birth to rich, dense clusters. We propose to take advantage of the high angular resolution and relatively wide field afforded by WFPC2 on HST to search for binary stars with angular separations of between 0.1" and 1" among a sample of about 120 stars located in 2 young (age approximately 1 Myr) clusters embedded within the nearest GMC: Orion (d = 460 pc). A sample this size will enable a statistically significant comparison between the binary frequency in the separation range 46 AU < r < 460 AU found for these young clusters, and that found for (1) older stars in the solar-neighborhood (expected binaries about 24/120); and (2) Taurus where most or all stars are binaries (expected binaries about 65/120). Our observations should thus provide a test of the hypothesis that all stars are born in binary/multiple systems, not only in regions like Taurus, but in rich clusters as well. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 0.40 par: 0 10. Num targs pri: 7 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: WF/PC ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5355 PI: Stephen E. Strom Proposal Title: THE BINARY FREQUENCY AMONG SOLAR-TYPE STARS IN YOUNG CLUSTERS: CYCLE4 HIGH ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Strom E. Stephen 2001 USA Suzan Edwards 2005 USA Catherine Dougados 5428 FRANCE X Patrick Hartigan 2001 USA Andrea Ghez 1210 USA Deborah L. Padgett 1002 USA Strom Karen 2001 USA Page 3 ------------------------------------------------------------------------------------ 3. Description of proposed observations. We propose to take advantage of the high angular resolution and relatively wide field afforded by WFPC2 on HST to search for binary/multiple stars with angular separations between 0.1" and 1" among a sample of about 250 stars in 3 young (age approximately 1 Myr) clusters. Our plan is to observe 7 fields through 2 filters: F814W and F547M. These observations will enable us to derive monochromatic luminosity ratios, colors and separations for the binary and multiple systems discovered in our survey. Because the young clusters which comprise our sample are still partially embedded within their natal molecular cores, member stars are expected to suffer extinctions between 1 and 20 mag. In order to maximize our sample size, we have chosen to image these clusters at a wavelength (lambda approximately 8500 angstroms) which both minimizes extinction and measures the flux at a wavelength near the Planck maximum for late-type stars; hence our choice of F814W. Our planned exposures will allow us to obtain F814W fluxes for stars as faint as I = 25 with S/N = 10. Because cluster members are expected to be no older than t aproximately 1 Myr, achieving this sensitivity will allow us to image primaries and secondaries with masses as small as the hydrogen-burning limit provided that extinction is less than 15 mag. Complementary observations through F547M will provide a color index, F814W/F547M. In combination with the flux ratio for each member of the pair measured through F814W, and a reddening to the system estimated from ground-based measurements, this index will enable an initial estimate of the relative masses for the binary components. Because the WF camera has a pixel size of 0.1", the diffraction-limited core will be undersampled even at wavelength of 8500 angstroms. Hence, in order to achieve high photometric accuracy at near diffraction-limited resolution, we plan to take 2 images of all fields, each displaced by 1/2 pixel. By summing these images, we can more effectively sample stellar images and recover information close to the diffraction-limited resolution of HST. A typical cluster field will include both bright unreddened stars near the earthward side of the molecular core, and faint heavily-reddened stars embedded within the core. We have thus designed our experiment to enable measurements of systems which span a wide range (about 12 mag) in I-band brightness. To do this, we plan to take two exposures through F814W. The first, of duration 1 sec, will permit us to observe the "bright" (I < 20 mag), lightly-reddened members of the clusters, while the second (of duration 100 s) will enable us to image stars as faint as I = 25 mag at S/N = 10. This strategy has the further advantage of enabling discovery of systems in which the components might have large mass (and thus, luminosity) ratios. We anticipate that we should be able to detect systems with flux ratios = 100 even if they have separations of 0.1". However, our ability to image faint companions near bright primaries at separations near the diffraction limit of HST will depend ultimately on the PSF achieved by WFPC2 and the details of CCD blooming and "bleeding". Hence, final assessment of the completeness of our survey for stars with separations of 0.1", and of the accuracy with which we can measure large flux ratios must await both evaluation of WFPC2 performance and subsequent modeling. We plan to take only one exposure of duration t = 1 sec with F547M. This decision is driven by observing efficiency considerations: our desire to complete our imaging of a region within an HST orbit. The practical consquence will be to limit our color survey to the brightest (I < 20) members of our sample. Page 4 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. 4a. The Need for HST The first advantage provided by HST results from its ability to resolve binary pairs and derive flux ratios at a wavelength (about 8500 angstroms) which lies (1) near the Planck maximum for late-type stars; and (2) near a minimum in the emission expected from accretion-related phenomena. By contrast, at 2.2 microns, where speckle techniques are most sensitive, the fluxes for T-Tauri stars surrounded by circumstellar accretion disks will include a large emission component arising from the disk. Thus, while speckle observations at 2.2 microns can provide information regarding relative accretion rates in binary pairs, and identify optically-invisible, infrared-bright companions, they cannot provide the accurate corrections for the contributions of unresolved companions to stellar luminosities required for reliable age and mass determinations. Such corrections must be made at a wavelength (about 1 micron) where the stellar photosphere dominates the observed flux. A second advantage derives from the ability of WFPC2 to image a large number of stars simultaneously. This is crucial because deciding whether all cluster stars form in binary systems requires observation of a large sample. By contrast, speckle- imaging observations must be carried out one star at a time, and moreover require observation of a nearby star to define a local point spread function. Speckle imaging of a sample 120 stars would require many hundred hours on a large telescope. The third advantage of HST derives from superior sensitivity. WF images through F814W will enable flux measurements (S/N = 10) for stars with masses at the hydrogen-burning limit even if they are obscured by 15 magnitudes of extinction. Under the best atmospheric conditions, new-generation speckle cameras will enable imaging of binaries with primary stars K < 11.5. For stars with age approximately 1 Myr located at d = 460 pc, this corresponds with mass about 0.2 solar masses. Stars with M about 0.08 solar masses will have K = 13.5 mag assuming no foreground extinction, and K = 15.0 with 15 mag of extinction, respectively 2 and 3.5 mag below the limit of speckle camera performance. We are currently carrying out extensive ground-based optical/infrared photometric and spectroscopic investigations of our 3 target clusters. HST observations will provide essential complementary information (I-band fluxes and separations for a large number of unresolved binaries in the separation range 46 AU < r < 460 AU) which will be crucial to full realization of our long term goals: (1) characterizing the IMFs for these clusters and the sequence in which stars of different masses form, and (2) understanding the frequency and evolutionary timescales for the circumstellar accretion disks. As described in section 2, these observations are prerequisites for accurate age and mass determinations, and for identifying the factors which control the evolution of circumstellar disks. R. Mathieu (private communication) has just initiated a survey for spectroscopic binaries in some of our target clusters. His survey will enable detection of binaries in the separation range (r < 10 AU) provided they are brighter than I = 15 mag. The Mathieu survey will thus not enable a comprehensive search for binaries over the full ranges of stellar masses which we anticipate observing with HST. However, in the magnitude range where the surveys overlap, the relative binary frequencies derived for close (r < 10 AU) and more distant (50 AU < r < 500 AU) pairs will enable comparison with identical statistics for older solar neighborhood stars, and thus provide the basis for evaluating the dynamical evolution of binary systems. 4b. Justify Exposure Times A large sample of stars must be observed in order to provide a robust test of the hypothesis that all solar-type stars form in binary/multiple systems. From examination of ground-based I-, J-, H- and K- band images of our target clusters, we have selected 7 fields which contain about 120 stars with I < 25 mag. Our exposure times of 1 sec and 100 sec through F814W enable us to image stars over the range 12 < I < 25 mag with S/N > 10 , while our exposure time of 1 sec through F547M enables us to image stars with 12 < V < 20 mag. The F814W exposures should thus permit a complete search for binaries with masses as small as the hydrogen-burning limit, provided that they are obscured by extinction of less than 15 mag and have ages t < 1 Myr. Colors, which enable rough estimates of mass ratios for binary pairs, can be derived for stars with V < 20 mag. Page 5 ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. ------------------------------------------------------------------------------------ 9. Description of previous HST work. The PI and a team of 14 researchers were initially awarded 20 hours of time during Cycle 1 to study the "Formation and Evolution of Solar Nebulae Surrounding Pre-Main Sequence Stars" (proposal number 2261). Our goal was to image scattered light from circumstellar disks surrounding a large sample of classical and weak- line T Tauri stars, and forbidden line emission from collimated jets driven by rapidly accreting TTS. A much scaled-down version of this program was approved in order to evaluate what fraction of the scientific goals could be accomplished with the degraded HST imaging capability. In the end, small but measurable orbit- to-orbit changes in the PSF, combined with the power carried in the wings of the PSF precluded detection of either low surface brightness disks, extended envelopes or sub-arcsecond jets. One of our images resolved a close binary (DF Tau; separation about 0.08") which had been detected previously via lunar occultation observations. This pair of stars have a projected separation placing them both inside the accretion disk inferred for the primary from observed infrared excesses. We are currently analyzing the images to assess whether one or both components is undergoing inner disk accretion (based on measuring the [O I] emission flux through the narrow band F631 N filter). Although no published results have yet come from our Cycle 1 data (please note that our last observations were not taken until December, 1992 some of the sophisticated analysis techniques we had hoped to bring to bear on our Cycle 1 observations on archived HST images of young stellar objects. We have just submitted an ApJ Letter (Kepner et al., 1993) in which we were able to reconstruct H alpha and [O I] images of the jet associated with DG Tau. The image restoration method used is based on the ``Half-Gaussian'' model and the corresponding ``Half-Quadratic'' algorithm. This newly developed method is described fully in Geman and Yang (1993), and was tailored for use with the HST data by members of the team we assembled to attempt recovery of the aberrated Cycle 1 images. Our reconstructed DG Tau images enable us to (1) show that collimation takes place within 30 AU of the stellar surface; (2) constrain the degree of collimation (the jet is unresolved in the direction perpendicular to its propagation axis); and (3) demonstrate that the jet has discernible knots, separated by 10s of AU, possibly indicative of episodic mass outflow. Broadly speaking, both involve study of young stellar objects, but the current proposal focuses on multiplicity of solar-type stars and has little or no overlap with our Cycle 1 proposal. PUBLICATIONS "Hubble Space Telescope Images of the Subarcsecond Jet in DG Tau" by J. Kepner, P. Hartigan, C. Yang, and S.E. Strom 1993, ApJ Letter, submitted. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). ------------------------------------------------------------------------------------ 11. Address Information Name: STEPHEN E. STROM Category: PI Institution: 2001 Address: FIVE COLLEGE ASTRONOMY DEPARTMENT/ UNIVERSITY OF MASSACHUSETTS, AMHERST 517G LEDERLE GRADUATE RESEARCH TOWER B City: AMHERST State: MA Zip Code: 01003 Country: USA Telephone: 413-525-2290 Telex (or e-mail): sstrom@donald.phast.umass.edu ------------------------------------------------------------------------------------ Page 6 Name: DEBORAH L. PADGETT Category: CON Institution: 1002 Address: 2939 N. MARENGO AVENUE City: ALTADENA State: CA Zip Code: 91001 Country: USA Telephone: 818-791-4818 Telex (or e-mail): dlp@lb6.jpl.nasa.gov ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 5355 [ 7] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC2068-POS1 C, RA = 5H 46M 44.749S +/- 2000.0 1 V = 20 +/- 5 204 0.3S, DEC = +0D 5' 21.43" +/- 5" Comments: THIS IS A T TAURI STAR CLUSTER, WITH AT LEAST 18 STARS FAINTER THAN MAGNITUDE 10 IN THE FIELD. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC2068-POS2 C, RA = 5H 46M 37.306S +/- 2000.0 1 V = 20 +/- 5 204 0.3S, DEC = +0D 6' 33.84" +/- 5" Comments: THIS IS A T TAURI STAR CLUSTER, WITH AT LEAST 18 STARS FAINTER THAN MAGNITUDE 10 IN THE FIELD. ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC2068-POS3 C, RA = 5H 46M 45.547S +/- 2000.0 1 V = 20 +/- 5 204 0.3S, DEC = +0D 3' 20.65" +/- 5" Comments: THIS IS A T TAURI STAR CLUSTER, WITH AT LEAST 18 STARS FAINTER THAN MAGNITUDE 10 IN THE FIELD. ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC2024-POS1 C, RA = 5H 41M 36.4S +/- 0.3S, 2000.0 1 V = 20 +/- 5 203 DEC = -1D 53' 54" +/- 5" Comments: THIS IS AN OB ASSOCIATION, WITH AT LEAST 30 STARS FAINTER THAN MAGNITUDE 10 IN THE FIELD. ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC2024-POS2 C, RA = 5H 41M 36.4S +/- 0.3S, 2000.0 1 V = 20 +/- 5 203 DEC = -1D 55' 30" +/- 5" Comments: THIS IS AN OB ASSOCIATION, WITH AT LEAST 30 STARS FAINTER THAN MAGNITUDE 10 IN THE FIELD. ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC2024-POS3 C, RA = 5H 41M 43.0S +/- 0.3S, 2000.0 1 V = 20 +/- 5 203 DEC = -1D 54' 39" +/- 5" Comments: THIS IS AN OB ASSOCIATION, WITH AT LEAST 30 STARS FAINTER THAN MAGNITUDE 10 IN THE FIELD. ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC2071 C, RA = 5H 47M 04.740S +/- 2000.0 1 V = 20 +/- 5 204 0.3S, DEC = +0D 21' 44.08" +/- 5" Comments: THIS IS A T TAURI STAR CLUSTER, WITH AT LEAST 15 STARS FAINTER THAN MAGNITUDE 10 IN THE FIELD. ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5355 [ 8] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1.1 DEFINE # WFPC2 IMAGE WFALL- F547M CLOCKS=NO 1 1S 10 1 1 CYCLE 4 BINPIC FIX ATD-GAIN=7 1S GROUP 1.1-1.3 NON- INT GROUP 1.1-1.6 NO GAP Comments: THIS IS A STAR CLUSTER FIELD WITH MANY STARS FAINTER THAN MAGNITUDE 10. THE BRIGHTEST STARS IN THE FIELD ARE EXPECTED TO SATURATE. THE S/N ESTIMATE IS FOR LATE-TYPE STARS WITH V = 20. POINTING AT DEFAULT TARGET POSITION. ------------------------------------------------------------------------------------------------------------------------------------ 1.2 DEFINE # WFPC2 IMAGE WFALL- F814W CLOCKS=NO 1 1S 10 1 1 CYCLE 4 BINPIC FIX ATD-GAIN=7 1S Comments: THIS IS A STAR CLUSTER FIELD WITH MANY STARS FAINTER THAN MAGNITUDE 10. THE BRIGHTEST STARS IN THE FIELD ARE EXPECTED TO SATURATE. THE S/N ESTIMATE IS FOR LATE-TYPE STARS WITH I = 25. POINTING AT DEFAULT TARGET POSITION. ------------------------------------------------------------------------------------------------------------------------------------ 1.3 DEFINE # WFPC2 IMAGE WFALL- F814W CLOCKS=YES 1 100S 10 1 1 CYCLE 4 BINPIC FIX ATD-GAIN=7 100S ------------------------------------------------------------------------------------------------------------------------------------ 1.4 DEFINE # WFPC2 IMAGE WFALL- F814W CLOCKS=YES 1 100S 10 1 1 CYCLE 4 BINPIC FIX ATD-GAIN=7 100S GROUP 1.4-1.6 NON- INT POS TARG +0.05, +0.05 Comments: THIS IS A STAR CLUSTER FIELD WITH MANY STARS FAINTER THAN MAGNITUDE 10. THE BRIGHTEST STARS IN THE FIELD ARE EXPECTED TO SATURATE. THE S/N ESTIMATE IS FOR LATE-TYPE STARS WITH I = 25. POINTING IS OFFSET +0.05" IN X AND Y. ------------------------------------------------------------------------------------------------------------------------------------ 1.5 DEFINE # WFPC2 IMAGE WFALL- F814W CLOCKS=NO 1 1S 10 1 1 CYCLE 4 BINPIC FIX ATD-GAIN=7 1S SAME POS FOR 1.5 AS 1.4 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5355 [ 9] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1.6 DEFINE # WFPC2 IMAGE WFALL- F547M CLOCKS=NO 1 1S 10 1 1 CYCLE 4 BINPIC FIX ATD-GAIN=7 1S SAME POS FOR 1.6 AS 1.4 Comments: THIS IS A STAR CLUSTER FIELD WITH MANY STARS FAINTER THAN MAGNITUDE 10. THE BRIGHTEST STARS IN THE FIELD ARE EXPECTED TO SATURATE. THE S/N ESTIMATE IS FOR LATE-TYPE STARS WITH I = 25. POINTING IS OFFSET +0.05" IN X AND Y. ------------------------------------------------------------------------------------------------------------------------------------ 10 USE NGC2068- PCS MODE F BINPIC POS1 ------------------------------------------------------------------------------------------------------------------------------------ 20 USE NGC2068- PCS MODE F BINPIC POS2 ------------------------------------------------------------------------------------------------------------------------------------ 30 USE NGC2068- PCS MODE F BINPIC POS3 ------------------------------------------------------------------------------------------------------------------------------------ 40 USE NGC2024- PCS MODE F BINPIC POS1 ------------------------------------------------------------------------------------------------------------------------------------ 50 USE NGC2024- PCS MODE F BINPIC POS2 ------------------------------------------------------------------------------------------------------------------------------------ 60 USE NGC2024- PCS MODE F BINPIC POS3 ------------------------------------------------------------------------------------------------------------------------------------ 70 USE NGC2071 PCS MODE F BINPIC ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5355 [ 10] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CLOCKS=NO ATD-GAIN=7 CLOCKS=YES ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 0.40 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COOL STARS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category EARLY EVOLUTION ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 4; GROUP 1.1-1.3 NON-INT; GROUP 1.1-1.6 NO GAP; CYCLE 4 GROUP 1.4-1.6 NON-INT; POS TARG +0.05, +0.05 SAME POS FOR 1.5 AS 1.4 SAME POS FOR 1.6 AS 1.4 PCS MODE F ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F547M F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC2068-POS1 NGC2068-POS2 NGC2068-POS3 NGC2024-POS1 NGC2024-POS2 NGC2024-POS3 NGC2071 ------------------------------------------------------------------------------------------------------------------------------------