9081( 5) - 02/19/02 13:03 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9081 Version: 5 Check-in Date: 19-Feb-2002 13:02:36 1.Proposal Title: Accretion in the planet-forming disks of the TW Hya association ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Nuria Calvet Smithsonian Institution Astrophysical Observatory CoI: Dr. Lee Hartmann Smithsonian Astrophysical Observatory N CoI: Dr. Paola D'Alessio American Museum of National History N CoI: Dr. James Muzerolle University of Arizona N CoI: Mr. Jose Luis Saucedo Smithsonian Astrophysical Observatory N ------------------------------------------------------------------------------------ 5. Abstract We propose to obtain STIS/MAMA high signal-to-noise, low resolution ultraviolet spectra of the only two stars in the ~ 10 Myr old TW Hya association that are still accreting to measure the mass accretion rate through their disks. With these measurements we will be able to assess the gas content in these disks which show clear signs that dust is rapidly evolving towards planetesimals and planets, and obtain crucial parameters to address the problems of planet migration and survival at 10 Myr, the time-scale for planet formation according to meteoritic and preliminary astronomical evidence. ------------------------------------------------------------------------------------ 9081( 5) - 02/19/02 13:03 - [ 2] Observations Description ------------------------ We propose to obtain STIS/MAMA spectra with gratings G140L and G230L. With these gratings, we will obtain continuum fluxes over the entire the UV region, from ~ 1150 Angstrom to 3200 Angstrom (the gratings coverage overlaps at ~ 1500 Angstrom). The resolution of the L gratings is low enough that we can reach signal-to-noise (S/N) >~ 10 with reasonable exposure times. This will allow us to obtain a reliable measure of the luminosity of the UV excess flux; with this luminosity and using our shock models (Calvet & Gullbring 1998; Gullbring et al. 2000), we will then obtain estimates of the accretion luminosity and mass accretion rate. Objects in the TWa are expected to be relatively bright in the UV because it is one of the closest star-forming regions (~ 50 pc) and interstellar reddening is negligible. For TW Hya, we have used the few existing long exposure IUE spectra to obtain the UV flux level and estimate the exposure time needed to obtain S/N >~ 10 in the continuum. These exposure times are ~ 1 min with G230L at Lambda = 2400 Angstrom and 30 minutes with G140L at Lambda = 1400 Angstrom, so we are requesting 1 orbit to obtain these spectra. To use as a template to obtain a comparison between the UV fluxes at two different ages and evolutionary properties, we also request to obtain spectra with similar setup for the Taurus TTS BP Tau. Preliminary modeling of the accretion shock in TW Hya indicates that the accretion columns carry a similar energy flux than that of BP Tau, but with a much smaller surface coverage of the columns (Gullbring et al. 2000; Muzerolle et al. 2000), yielding a difference in mass accretion rate of a factor of ~ 100. Comparison between these two full- wavelength coverage UV continuum fluxes will allow us to gain more insight into the physical properties of the accretion columns and into the process of mass loading onto the star. Although BP Tau is ~ 3 times as far and has some reddening (A_V = 0.5), it is so much intrinsically brighter in the UV (as determined by existing, low S/N IUE spectra) that its UV fluxes are very similar to those of TW Hya, so we require 1 orbit for this star as well. No UV spectrum is available for Hen3-600A. However, modeling of the optical magnetospheric emission lines indicates that the mass accretion rate is 10 times lower or more than that of TW Hya. Scaling down from the UV fluxes of this star, we would require an exposure time of ~ 1 hour to obtain S/N=10 at 1800 Angstrom with G230L for Hen3-600A. The exposure time to obtain a significant signal with G1140L is too long, so we will concentrate on the NUV fluxes, obtaining a wavelength coverage from 1800 Angstrom to 3000 Angstrom. We are requesting 2 orbits to observe Hen3- 600A, allowing for the case that we have overestimated the mass accretion rate. Since the expected accretion luminosity of Hen3-600A is low, the intrinsic stellar chromospheric emission may be an important contributor to the UV fluxes, so we must obtain UV spectra of a star which is not accreting, but otherwise is at similar stage of evolution than Hen3-600A to use as template. For this purpose, we plan to observe another star of TWa, TWa10, which has a narrow HAlpha profile in our Keck spectrum (cf. Figure 2, left), and so is definitely not accreting. TWa10 has a spectral type similar to Hen3-600A (M2.5 and M3, Webb et al. 1999); in addition, our spectrum indicates that it is not a spectroscopic binary nor is it rapidly rotating. We estimate that we can reach the M2 photosphere with S/N ~ 7 with two orbits, but since we are mainly interested in the continuum level, we can improve the S/N by averaging out over several resolution elements (~ 3 Angstrom for G230L). Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9081( 5) - 02/19/02 13:03 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 TW-HYA STAR, T TAURI STAR RA=11H 1M 51.95S +/- 0.4", DEC=- J2000 V = 11.1+/-0.5 34D 42' 17.7" +/- 0.41", PLATE- F-CONT-BKG(3500)=6+/-3e-14 ID=0482 F-CONT-BKG(3000)=5+/-2e-14 F-CONT-BKG(2500)=3+/-1e-14 F-CONT-BKG(2000)=2+/-1e-14 F-CONT-BKG(1500)=40+/-30e-16 TYPE=K7 Coordinate Source: GUIDE_STAR_CATALOG 2 HEN3-600A STAR, T TAURI STAR RA=11H 10M 28.01S +/- 0.5", DEC= J2000 V = 11.9+/-0.5 -37D 31' 52.9" +/- 0.41", PLATE- TYPE=M3 ID=0028 Coordinate Source: GUIDE_STAR_CATALOG Comments: Interpretation of magnetospheric indicators (Muzerolle et al 2000, ApJ 535, L47) suggests that the UV flux of Hen3-600A will be 10 - 20 times fainter than in TW Hya (Target 1) 3 TW-10 STAR, T TAURI STAR RA=12H 35M 4.39S +/- 0.4", DEC=- J2000 V = 12.6+/-0.5 41D 36' 38.7" +/- 0.34", PLATE- TYPE=M2.5 ID=00ZD Coordinate Source: GUIDE_STAR_CATALOG 4 BP-TAU STAR, T TAURI STAR RA=04H 19M 15.86S +/- 0.3", J2000 V = 12+/-0.5 DEC=29D 6' 27.2" +/- 0.3", PLATE F-CONT-BKG(3000)=20+/-15e-15 -ID=0051 F-CONT-BKG(2000)=60+/-50e-16 TYPE=K7 Coordinate Source: GUIDE_STAR_CATALOG 9081( 5) - 02/19/02 13:03 - [ 4] Visit: 01 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 TW-HYA STIS/C ACQ F28X50O MIRROR ACQTYPE=POINT 1 3 S CD III ------------------------------------------------------------------------------------------------------------------------------------ 20 TW-HYA STIS/N ACCUM 52X2 G230L 2376 1 1 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 30 TW-HYA STIS/F ACCUM 52X2 G140L 1425 1 30 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9081( 5) - 02/19/02 13:03 - [ 5] Visit: 02 Visit Priority: Visit Requirements: ORIENT 47.5D TO 110D ORIENT 227.5D TO 290D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 HEN3-600A STIS/C ACQ F28X50O MIRROR ACQTYPE=POINT 1 5 S CD III ------------------------------------------------------------------------------------------------------------------------------------ 20 HEN3-600A STIS/N ACCUM 52X2 G230L 2376 1 37 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 30 HEN3-600A STIS/N ACCUM 52X2 G230L 2376 1 37 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9081( 5) - 02/19/02 13:03 - [ 6] Visit: 03 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 BP-TAU STIS/C ACQ F28X50O MIRROR ACQTYPE=POINT 1 6 S CD III ------------------------------------------------------------------------------------------------------------------------------------ 20 BP-TAU STIS/N ACCUM 52X0.2 G230L 2376 1 1 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 30 BP-TAU STIS/F ACCUM 52X0.2 G140L 1425 1 30 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9081( 5) - 02/19/02 13:03 - [ 7] Visit: 04 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 TW-10 STIS/C ACQ F28X50O MIRROR ACQTYPE=POINT 1 6 S CD III ------------------------------------------------------------------------------------------------------------------------------------ 20 TW-10 STIS/N ACCUM 52X2 G230L 2376 1 34 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 30 TW-10 STIS/N ACCUM 52X2 G230L 2376 1 34 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9081( 5) - 02/19/02 13:03 - [ 8] Summary Form for Proposal 9081 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50OIII 52X2 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 47.5D TO 110D ORIENT 227.5D TO 290D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G230L G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names TW-HYA HEN3-600A BP-TAU TW-10 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 2376 1425 ------------------------------------------------------------------------------------------------------------------------------------