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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
High Resolution 4.7 m Keck/NIRSPEC Spectra of Protostars

Adwin Boogert

Geoff Blake

Caltech/OVRO

Caltech/OVRO

nirspec at keck ii
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
source sample
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.
r 25 000 4 7 m spectra c2d irs ysos
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.
l1489 irs with keck nirspec
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

:

the shrinking disk of l1489 irs
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)

the shrinking disk of l1489 irs1
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)

the shrinking disk of l1489 irs2
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)

the shrinking disk of l1489 irs3
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)

the shrinking disk of l1489 irs4
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)