An Effective Temperature Scale for Late-M and L Dwarfs, from Resonance Absorption Lines of Cs I and Rb I

By G. Basri, S. Mohanty, F. Allard, Peter Hauschildt, X. Delfosse, E. Martín, T. Forveille, B. Goldman. 2000

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We present Keck HIRES spectra of six late-M dwarfs and 11 L dwarfs. Our goal is to assign effective temperatures to the objects using detailed atmospheric models and fine analysis of the alkali resonance absorption lines of Cs I and Rb I. These yield mutually consistent results (±50 K) when we use "cleared-dust" models, which account for the removal of refractory species from the molecular states but do not include dust opacities. We find a tendency for the Rb I line to imply a slightly higher temperature, which we ascribe to an incomplete treatment of the overlying molecular opacities. The final Teff we adopt are based on the Cs I fits alone, though the Rb I fits support the Cs I temperature sequence. This work, in combination with results from the infrared, hints that dust in these atmospheres has settled out of the high atmosphere but is present in the deep photosphere. We also derive radial and rotational velocities for all the objects, finding that the previously discovered trend of rapid rotation for very low mass objects is quite pervasive. To improve on our analysis, there is a clear need for better molecular line lists and a more detailed understanding of dust formation and dynamics.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/6bdf804a494bb35f7002296fdaf823b35841daba

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Citations in the corpus

Flaring up All Over—Radio Activity in Rapidly Rotating Late M and L Dwarfs (2001, background): “The upper limit on the radio activity from the fast rotator Kelu 1 (Krishnamurthi, Leto & Linsky 1999), with vsini ≈ 60 km sec−1 (Basri et al. 2000) is three times higher than the detected fast rotators, and therefore does not constraithe possible relation between radio activity and rotational…”
Very Low Mass Stars and Brown Dwarfs in Taurus-Auriga (2002, methodology): “The data were reduced in a standard fashion for echelle data using IDL routines as described in Basri et al. (2000).”
THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS (2016, unknown): “— (1) This work; (2) Allers et al. (2007); (3) Allers & Liu (2013a); (4) Basri et al. (2000); (5) Bouvier et al. (2008); (6) Cruz et al. (2003); (7) Cruz et al. (2007); (8) Cruz et al. (2009); (9) Faherty et al. (2009); (10) Faherty et al. (2012); (11) Faherty et al. (2013); (12) Gagné et al.…”
Spitzer IRAC Photometry of M, L, and T Dwarfs (2006, background): “…and several dozen T dwarfs have now been identified, leading to well-defined L and Tspectral sequences (Kirkpatrick 2005) and to a large body of accurate photometry and quantitative spectroscopy to characterize those spectral types (Leggett et al. 2001, 2002; Basri et al. 2000; Reid et al. 2002).”
Hubble Space Telescope Observations of Binary Very Low Mass Stars and Brown Dwarfs (2003, unknown): “This supported by the scarcity of double-lined binaries detected in highresolution studies of L dwarfs (Basri et al. 2000; Schweitzer et al. 2001).”
A Search for L Dwarf Binary Systems (2000, methodology): “Basri et al. (2000) have combined model atmosphere calculations with high-resolution line profiles to derive temperatures of ∼ 2200K for spectral type L0 and ∼ 1700K for type L8 (K99 classification system).”
VOSA: Virtual Observatory SED Analyzer. An application to the Collinder 69 open cluster (2008, methodology): “…the Md factor and assuming a typical radius for 1-5 Gyr dwarfs with the given temperature of 1600 K (according to isochrones from Baraffe et al. 2003), we estimate a distance to this object between 61 and 69 parsecs and a spectral type of L6-L7 according to the Teff scale by Basri et al. (2000).”
New spectral types L and T (2005, background): “Although others have proposed classifications in which the goal was to incorporate theory into the scheme (Basri et al. 2000) or in which a single index was the primary classification criterion (Martı́n et al. 1999), these schemes have been little used.”
Multiplicity of Nearby Free-floating Ultracool Dwarfs: A Hubble Space Telescope WFPC2 Search for Companions (2003, background): “Basri et al. (2000) estimated this temperature to be Teff = 1700– 1800 K. Tokunaga & Kobayashi (1999) also observed absorption feature in the spectra but attributed it to H2 rather than CH4.”
The Spectra of T Dwarfs. I. Near-Infrared Data and Spectral Classification (2001, background): “We compare this relation to the Kirkpatrick et al. (1999, 2000) and Basri et al. (2000) L dwarf temperature scales (solid lines) in Figure 17, where the latter scale has been adjusted to the Kirkpatrick et al. (1999) L dwarf types using transformations given in Mart́ın et al. (1999).”
Astrometry and Photometry for Cool Dwarfs and Brown Dwarfs (2002, methodology): “5 on the Kirkpatrick system), with Teff values primarily from the work of Basri et al. (2000).”
Characterization of M, L, and T Dwarfs in the Sloan Digital Sky Survey (2002, background): “These discoveries culminated in the definition of the L spectral class (Kirkpatrick et al. 1999, hereafter K99; Martin et al. 1999; Kirkpatrick et al. 2000, hereafter K00; Basri et al. 2000).”
AN EMPIRICAL UBV RI JHK COLOR–TEMPERATURE CALIBRATION FOR STARS (2006, methodology): “For the coolest dwarfs, analysis of the data of Basri et al. (2000) yielded a relation as a function of I−K color, specifically Teff = −460.25×(I −K)+4323, valid for I − K > 2.9.”
L′ and M′ Photometry of Ultracool Dwarfs (2004, background): “Mart́ın et al. (1999b) and Basri et al. (2000) derived a warmer Teff scale by fitting synthetic absorption profiles of Rb I λ7948 Å and Cs I λ8521 Å with those observed in their optical spectra.”
Activity in Very Cool Stars: Magnetic Dissipation in Late M and L Dwarf Atmospheres (2002, background): “Profile-fitting of the observed atomic resonance lines of alkali metals in the optical spectrum of L dwarfs indicates that grains may have gravitationally settled out of the atmosphere (Basri et al. 2000)4, and can thus be ignored.”
The T Tauri Phase Down to Nearly Planetary Masses: Echelle Spectra of 82 Very Low Mass Stars and Brown Dwarfs (2005, methodology): “The data were reduced in standard fashion with IDL routines, as described in Basri et al. (2000).”
The First Substellar Subdwarf? Discovery of a Metal-poor L Dwarf with Halo Kinematics (2003, methodology): “Solar-metallicity mid- to late-type L dwarfs have temperatures 1400dTeffd1800 K (Kirkpatrick et al. 1999; Basri et al. 2000; Pavlenko, Zapatero Osorio, & Rebolo 2000; Leggett et al. 2001; Stephens et al. 2001; Burgasser et al. 2002; Dahn et al. 2002).”
Infrared Spectra and Spectral Energy Distributions of Late M and L Dwarfs (2000, methodology): “Basri et al. (2000) use Ames-Cond NEXTGEN model Ðts to rubidium and cesium lines and derive e†ective temperatures within 100 K of our spectral synthesis values for Kelu-1, Denis-P J1058[1548, and Denis-P J1228[1547AB; they derive a value 150 K lower than ours for the coolest object in common,…”