7311( 3) - 03/26/97 10:01 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7311 Version: 3 Check-in Date: 26-Mar-1997 09:57:49 1.Proposal Title: Spectroscopic Imaging of DG Tau -- Clues to the Structure and Collimation of T Tauri Star Winds ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle YOUNG STARS AND CIRCU GO 7 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: RANHARD MUNDT MPI FUR ASTRONOMIE CoI: Thomas Ray Dublin Institute for Advanced Studies N CoI: Max Camenzind Landessternwarte Heidelberg N CoI: Jochen Eisloeffel Thuehringer Landessternwarte Tautenburg N CoI: Gerhard Hirth Max-Planck-Institut fuer Astronomie N CoI: Josef Solf Thuehringer Landessternwarte Tautenburg N ------------------------------------------------------------------------------------ 6. Abstract We propose to investigate the complex small-scale (<= 1'') dynamical and morphological structure of the collimated outflow from the classical T Tauri (cTTS) star DG Tau using spectroscopic imaging in HAlpha and all of its strong red forbidden emission lines. Seven overlapping slit positions, parallel to the outflow but with appropriate offsets in the transverse direction, will be used to provide 2- D intensity and radial velocity data on the high velocity component (HVC or jet component) and the low velocity (LVC) component of the outflow. With this single, but very suitable, target we wish to attack a number of fundamental questions, generic to outflows from all young stars: 1. What is the nature of the enigmatic LVC observed in the forbidden emission lines of cTTSs? This component is spatially much more compact than the jet component (offset typically 0.1''--0.4'' from the star) and represents only partially ionized gas which is flowing ~10 times slower than the jet. Understanding the origin of this component will have enormous consequences for models of magneto-centrifugally driven outflows, since hints for broadening of this component by rotation have already been found in ground-based data. 2. What is the spatial intensity, velocity and excitation structure of these flows on 0.1''--2'' scales, e.g.\ is there evidence for entrainment and velocity variations? 3. What does the transverse velocity profile of a stellar jet look like? Is there evidence, close to the star, for a boundary layer in the jet? 4. On what scales are jets from young stars collimated? ------------------------------------------------------------------------------------ 7311( 3) - 03/26/97 10:01 - [ 2] Observations Description ------------------------ For our long-slit spectroscopic imaging of DG Tau we propose to use the G750M grating of STIS at the so-called ``secondary tilt'' centered at 6581 Angstrom. This would cover the range from 6295 Angstrom to 6867 Angstrom and will allow us to obtain spectra covering HAlpha and all strong red FELs. We propose a slit width of 0.1''. From ground-based observations the direction of the blueshifted outflow is known to be at PA=226 degrees (Mundt, Brugel, and Buhrke 1987; ApJ 319, 275). Obviously the slit of STIS will be oriented at this position angle (i.e. ORIENT = 91 degrees) and a tolelerance of +- 1 degree in position angle would be acceptable for this well-collimated jet. In order to image the outflow also in its transverse direction with the appropriate sampling of the point spread function we propose to use seven slit positions. One slit will be placed directly through the star and the other six will be offset perpendicular to the outflow direction in steps of +/-0.07'' (i.e. the slits we offset towards PA=136^degrees and 316 degrees, respectively by 0.07'', 0.14'' and 0.21''). This mean explicitly that we have the following offsets relative to the star and perpendicular to the slit lenght for the individual exposures: exposure 30 and 40: X=-0.21 arcsec exposure 50: X=-0.14 arcsec exposure 60: X=-0.07 arcsec exposure 70: X=0.0 arcsec; i.e. slit positioned on the star exposure 80: X=+0.07 arcsec exposure 90: X=+0.14 arcsec exposure 100: X=+0.21 arcsec We do not regard more slit positions necessary for an investigation of the jet within 1'' from the star, since as outlined above, the jet has probably a width of about 0.3'' at 1'' distance. Our exposure times are largely determined by the flux in the [NII] Lambda6583 line which is a rather important line for excitation studies and which has about a 15 times smaller integrated line flux than the [OI] Lambda 6300 line (Hartigan et al. 1995, ApJ, 452, 736). From the line fluxes given by the latter authors and assuming a 0.3'' x 2'' sized emission region, one gets a [NII] Lambda6583 surface brightness of 10^-13 erg s^-1 cm^-2 arcsec^-2 AA^-1 (for a 3 Angstrom broad line). With these numbers, and using the STIS Exposure Time Calculator, we find that for an integration time of 2700 sec (3 way cosmic ray split of one orbit i.e. 3x900s) one gets a S/N ratio of about 70 in regions free of stellar continuum emission. The S/N ratio, however, will decrease to about 8 nearer the star, where the stellar continuum becomes the dominant noise source. Note that the star will not be saturated in our images and it will therefore not be a problem to subtract the stellar continuum contribution from the spectra. Note also that we have assumed the star has a spectral type of K3V as given in the literature. Thus in summary, one orbit per slit position will provide data us with a sufficient S/N ratio and 7 orbits in total are required. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7311( 3) - 03/26/97 10:01 - [ 3] Data Distribution Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7311( 3) - 03/26/97 10:01 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 DGTAU STAR,K V-IV,T TAURI RA=4H 27M 4.71S +/- .3",DEC=26D J2000 V = 12.1+/-0.5 STAR,ISM,HERBIG-HARO 6' 16.8" +/- 0.3",PLATE-ID=000L TYPE=K7V OBJECT,JET,COMETARY B-V = 0.9+/-0.2 NEBULA SURF-LINE(6583)=10+/-3e-13 Comments: jet has a position angle of 226 degrees and extends about 10 arcsec from the star 7311( 3) - 03/26/97 10:01 - [ 5] Visit: 01 Visit Requirements: ORIENT 91D TO 91D 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 DGTAU STIS/C ACQ F28X50O MIRROR ACQTYPE=POINT 1 20 S ONBOARD ACQ FOR 20-100 CD III ------------------------------------------------------------------------------------------------------------------------------------ 20 DGTAU STIS/C ACQ/PEA 52X0.1 MIRROR 1 60 S ONBOARD ACQ FOR 30-100 CD K ------------------------------------------------------------------------------------------------------------------------------------ 30 DGTAU STIS/C ACCUM 52X0.1 G750M 6581 CR-SPLIT=NO,BINAXIS1=1,BINAXIS2=1 1 19 M POS TARG -0.21,0.0 CD ,GAIN=1 Comments: Slit offset relative to the star and perpendicular to the outflow direction (i.e. slit) by X=-0.21 arcsec ------------------------------------------------------------------------------------------------------------------------------------ 40 DGTAU STIS/C ACCUM 52X0.1 G750M 6581 CR-SPLIT=NO,BINAXIS1=1,BINAXIS2=1 1 13 M SAME POS AS 30 CD ,GAIN=1 Comments: Slit offset relative to the star and perpendicular to the outflow direction (i.e. slit) by X=-0.21 arcsec ------------------------------------------------------------------------------------------------------------------------------------ 50 DGTAU STIS/C ACCUM 52X0.1 G750M 6581 CR-SPLIT=2,BINAXIS1=1,BINAXIS2=1, 1 33 M POS TARG -0.14,0.0 CD GAIN=1 Comments: Slit offset relative to the star and perpendicular to the outflow direction (i.e. slit) by X=-0.14 arcsec ------------------------------------------------------------------------------------------------------------------------------------ 60 DGTAU STIS/C ACCUM 52X0.1 G750M 6581 CR-SPLIT=3,BINAXIS1=1,BINAXIS2=1, 1 45 M POS TARG -0.07,0.0 CD GAIN=1 Comments: Slit offset relative to the star and perpendicular to the outflow direction (i.e. slit) by X=-0.07 arcsec ------------------------------------------------------------------------------------------------------------------------------------ 70 DGTAU STIS/C ACCUM 52X0.1 G750M 6581 CR-SPLIT=3,BINAXIS1=1,BINAXIS2=1, 1 45 M POS TARG 0.0,0.0 CD GAIN=1 Comments: Slit centered directly on the star ------------------------------------------------------------------------------------------------------------------------------------ 80 DGTAU STIS/C ACCUM 52X0.1 G750M 6581 CR-SPLIT=3,BINAXIS1=1,BINAXIS2=1, 1 45 M POS TARG 0.07,0.0 CD GAIN=1 Comments: Slit offset relative to the star and perpendicular to the outflow direction (i.e. slit) by X=+0.07 arcsec ------------------------------------------------------------------------------------------------------------------------------------ 90 DGTAU STIS/C ACCUM 52X0.1 G750M 6581 CR-SPLIT=3,BINAXIS1=1,BINAXIS2=1, 1 45 M POS TARG 0.14,0.0 CD GAIN=1 Comments: Slit offset relative to the star and perpendicular to the outflow direction (i.e. slit) by X=+0.14 arcsec ------------------------------------------------------------------------------------------------------------------------------------ 7311( 3) - 03/26/97 10:01 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 100 DGTAU STIS/C ACCUM 52X0.1 G750M 6581 CR-SPLIT=3,BINAXIS1=1,BINAXIS2=1, 1 45 M POS TARG 0.21,0.0 CD GAIN=1 Comments: Slit offset relative to the star and perpendicular to the outflow direction (i.e. slit) by X=+0.21 arcsec ------------------------------------------------------------------------------------------------------------------------------------ 7311( 3) - 03/26/97 10:01 - [ 7] Summary Form for Proposal 7311 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT GAIN=1 BINAXIS2=1 BINAXIS1=1 CR-SPLIT=3 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category YOUNG STARS AND CIRCUMSTELLAR MATERIAL ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 91D TO 91D ONBOARD ACQ FOR 20-100 ONBOARD ACQ FOR 30-100 POS TARG -0.21,0.0 SAME POS AS 30 POS TARG -0.14,0.0 POS TARG -0.07,0.0 POS TARG 0.0,0.0 POS TARG 0.07,0.0 POS TARG 0.14,0.0 POS TARG 0.21,0.0 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G750M ------------------------------------------------------------------------------------------------------------------------------------ Target Names DGTAU ------------------------------------------------------------------------------------------------------------------------------------