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High Resolution 4.7  m Keck/NIRSPEC Spectra of Protostars

High Resolution 4.7  m Keck/NIRSPEC Spectra of Protostars. Adwin Boogert Geoff Blake. Caltech/OVRO Caltech/OVRO. NIRSPEC at Keck II. R=25,000 in 0.43” wide slit;  v=12 km/s at 4.7  m M band sensitivity: S/N=50 at M=5.6 magn in 900 seconds on source

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High Resolution 4.7  m Keck/NIRSPEC Spectra of Protostars

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  1. High Resolution 4.7 m Keck/NIRSPEC Spectra of Protostars Adwin Boogert Geoff Blake Caltech/OVRO Caltech/OVRO

  2. NIRSPEC at Keck II • R=25,000 in 0.43” wide slit; v=12 km/s at 4.7 m • M band sensitivity: S/N=50 at M=5.6 magn in 900 seconds on source • 3 partial orders on 10242 array. • Instantaneous coverage 0.07 m per order. • 4 settings needed to cover best part of atmospheric M band • NIRSPEC is powerful instrument for M band observations, although it is not optimized for M band

  3. The Atmosphere at 4.7 m at R=25,000

  4. The Atmosphere at 4.7 m at R=25,000

  5. Source Sample • Program start-up involved well known Herbig AeBe, T Tauri and Class I protostars in multiple settings. • Efficiency and success rate increase significantly with larger sample of sources in only one setting, initially. Follow-up in other settings on most interesting sources. • In second stage of program a flux limited sample drawn from the SIRTF/IRS c2d source list: M<7 magn, Dec > -30 degrees. Differences with VLT/ISAAC: • NIRSPEC only Dec > -30, so no R CrA, Cham, Lupus :( • NIRSPEC has higher spectral resolution (25000 vs. 10000) • Keck/NIRSPEC cannot observe sources without optical guide star closeby (4 arcmin), i.e. cannot do most embedded 'icy' sources. Bias toward more evolved sources with emission lines.

  6. R=25,000 4.7 m Spectra Trace Wide Variety of Phenomena

  7. R=25,000 4.7 m Spectra c2d/IRS YSOs • Status: • 2.5 good nights in spring/summer 2002 in which about 25 sources done. • Another run next week.

  8. L1489 IRS with Keck/NIRSPEC • Inventory: • deep 12CO gas absorption lines with red shifted wings • gas phase 13CO • gas phase C18O • complex CO ice band • no strong “XCN” • no strong H I Pf  • no CO emission :

  9. The Shrinking Disk of L1489 IRS HCO+ 3-2 OVRO/BIMA: • Class I SED • L=3.7 Lsun • Mdisk=0.02 Msun • Large flattened structure in millimeter continuum+line emission. • Continuum and lines cannot be fitted with same inside-out collapse model • Instead, velocity structure indicates large 2000 AU radius close to edge-on disk, in almost Keplerian rotation with infall component. Hogerheijde, ApJ 553, 618 (2001)

  10. The Shrinking Disk of L1489 IRS HCO+ 3-2 OVRO/BIMA: • L1489 IRS disk characterized by power law ‘flared disk’ model: • Fits lines, continuum and velocity structure. • T = 34(R/1000AU)-0.4 [K] • n = n0(R/1000AU)-1.5.exp(-z2/h2) [kg/cm3] • h = R/2 ‘flaring’ • Vin = 1.3(R/100AU)-0.5 [km/s] in addition to Keplerian rotation around 0.65 Msun central star • L1489 IRS represents short lived (<20,000 yr) transition phase in which disk shrinks to few 100 AU TTauri disk? Hogerheijde, ApJ 553, 618 (2001)

  11. The Shrinking Disk of L1489 IRS! CO Keck/NIRSPEC: • To first order, 4.7 m CO spectra confirm infalling motion of disk. • CO lines confine T and n structure of disk. • Introduce power law for density along pencil absorption beam: • n(l) = n0(l/1000 AU)-p Boogert et al., ApJ 568,761 (2002)

  12. The Shrinking Disk of L1489 IRS! CO Keck/NIRSPEC: • To first order, 4.7 m CO spectra confirm infalling motion of disk. • CO lines confine T and n structure of disk. • Introduce power law for density along pencil absorption beam: • n(l) = n0(l/1000 AU)-p • we find: p=0.55 • …scale height increases more than linear, very flared disk • Too much warm gas at high velocity Boogertet al., ApJ 568,761 (2002)

  13. The Shrinking Disk of L1489 IRS! CO Keck/NIRSPEC: • Modelled depth in better agreement if 50% of observed continuum from scattered light, not absorbed by CO. • Still too much warm gas at high velocity. • Only partial collapse of disk, e.g. a surface layer and outer parts? • Supported by low luminosity and weakness of H I emission lines (weak accretion shock): • 0.02 Msun disk collapse in 20000 yr gives Macc=10-6 Msun/yr or Lacc=7 Lsun, while L=3.7 Lsun. Boogert et al., ApJ 568,761 (2002)

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