The NIRSPEC Brown Dwarf Spectroscopic Survey. I. Low-Resolution Near-Infrared Spectra

By I. McLean, M. R. McGovern, A. Burgasser, J. D. Kirkpatrick, L. Prato, Sung Soo Kim. 2003

275 citations recorded by the source corpus.

We present the first results of a near-infrared (0.96-2.31 μm) spectroscopic survey of M, L, and T dwarfs obtained with NIRSPEC on the Keck II telescope. Our new survey has a resolving power of R = λ/Δλ ~ 2000 and is comprised of two major data sets: 53 J-band (1.14-1.36 μm) spectra covering all spectral types from M6 to T8 with at least two members in each spectral subclass (wherever possible), and 25 flux-calibrated spectra from 1.14 to 2.31 μm for most spectral classes between M6 and T8. Sixteen of these 25 objects have additional spectral coverage from 0.96 to 1.14 μm to provide overlap with optical spectra. Spectral flux ratio indexes for prominent molecular bands are derived, and equivalent widths (EWs) for several atomic lines are measured. We find that a combination of four H2O and two CH4 band strengths can be used for spectral classification of all these sources in the near-infrared and that the H2O indexes are almost linear with spectral type from M6 to T8. The H2O indexes near 1.79 and 1.96 μm should remain useful beyond T8. In the near-infrared a notable feature at the boundary between the M and L types is the disappearance of relatively weak (EW ~ 1-2 Å) atomic lines of Al I and Ca I, followed by Fe I around L2. At the boundary between L and T dwarfs it is the appearance of CH4 in all near-infrared bands (J, H, and K) that provides a significant spectral change, although we find evidence of CH4 as early as L7 in the K band. The FeH strength and the equivalent width of the K I lines are not monotonic, but in combination with other factors provide useful constraints on spectral type. The K I lines are sensitive to surface gravity. The CO band strength near 2.30 μm is relatively insensitive to spectral class. The peak calibrated flux (Fλ) in the 0.96-2.31 μm region occurs near 1.10 μm at M6 but shifts to about 1.27 μm at T8. In addition, the relative peak flux in the J, H, and K bands is always in the sense J > H > K except around L6, where the differences are small. One object, 2MASS 2244+20 (L6.5), shows normal spectral behavior in the optical but has an infrared spectrum in which the peak flux in J band is less than at H and K.

Subfields: Astronomy and Astrophysics, Instrumentation

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In Astronomy and Astrophysics

1. A. Burgasser
2. Michael C. Liu
3. J. D. Kirkpatrick
4. M. Marley
5. T. Dupuy
6. Jon Fortney
7. K. Luhman
8. Kelle Cruz

In Instrumentation

1. A. Burgasser
2. Michael C. Liu
3. J. D. Kirkpatrick
4. T. Dupuy
5. M. Marley
6. Kelle Cruz
7. Jon Fortney
8. K. Luhman

Citations in the corpus

• The 2MASS Wide-Field T Dwarf Search. III. Seven New T Dwarfs and Other Cool Dwarf Discoveries (2004, methodology): “5 2MASS 0516−0445 (for which only low S/N data have been obtained), these are the strongest K I lines measured in any T dwarf to date (Burgasser et al. 2002; Burgasser, McElwain, & Kirkpatrick 2003; McLean et al. 2003).”
• Discovery of Two Nearby Peculiar L Dwarfs from the 2MASS Proper-Motion Survey: Young or Metal-Rich? (2008, methodology): “We employed standard reductions using the REDSPEC package, as described in detail in McLean et al. (2003).”
• FURTHER DEFINING SPECTRAL TYPE “Y” AND EXPLORING THE LOW-MASS END OF THE FIELD BROWN DWARF MASS FUNCTION (2012, background): “Our brown dwarf candidates were observed in either or both of the N3 and N5 configurations (see McLean et al. 2003) that cover part of the J-band window from 1.15 to 1.35 µm and part of the H-band window from 1.5 to 1.8 µm.”
• Meeting the Cool Neighbors. IX. The Luminosity Function of M7-L8 Ultracool Dwarfs in the Field (2006, background): “McLean et al. (2003) acquired a J -band spectrum of 2M 1300+19 and noted that this object has “the highest equivalent widths in K I of any L1, or indeed almost any other L type.””
• The Spectroscopically Determined Substellar Mass Function of the Orion Nebula Cluster (2004, background): “The exceptions are the NaI lines which increase in strength until late M stars and then disappear quickly by early L (see also McLean et al. 2003, 2000 and Reid et al. 2001).”
• Binaries and the L Dwarf/T Dwarf Transition (2006, background): “…2002a; McLean et al. 2003); a restrengthening of J-band K i lines after weakening considerably in the latest type L dwarfs (Burgasser et al. 2002b; McLean et al. 2003; Cushing et al. 2005); and enhanced CO absorption at 4.7 m, possibly due to vertical upwelling (Noll et al. 1997; Oppenheimer et…”
• Near-Infrared Photometry and Spectroscopy of L and T Dwarfs: The Effects of Temperature, Clouds, and Gravity (2004, methodology): “The increase in K i equivalent widths for these dwarfs is confirmed by the higher resolution NIRSPEC data of McLean et al. (2003).”
• DETECTING PLANETS AROUND VERY LOW MASS STARS WITH THE RADIAL VELOCITY METHOD (2009, methodology): “The spectra reproduce the data shown by McLean et al. (2003) and Cushing et al. (2005) reasonably well when degraded to low-resolution.”
• The UKIRT Infrared Deep Sky Survey ZY JHK photometric system: passbands and synthetic colours (2006, background): “…Skrutskie (1997), Kirkpatrick et al. (1999b), Kirkpatrick et al. (2000), Knapp et al. (2004), Leggett et al. (2000; 2001; 2002a; 2002b), Liebert et al. (2000), McLean et al. (2003), Reid et al. (2001), Schultz et al. (1998), Strauss et al. (1999), Tinney et al. (1998), and Tsvetanov et al. (2000).”
• Global Climate and Atmospheric Composition of the Ultra-hot Jupiter WASP-103b from HST and Spitzer Phase Curve Observations (2018, background): “…been defined to characterize features in brown dwarf spectra, and these indices have revealed trends in the amplitude of a range of spectral features (water, sodium, potassium, VO, and FeH) with surface gravity and effective temperature (Reid et al. 2001; Geballe et al. 2002; McLean et al. 2003).”
• METALLICITY AND TEMPERATURE INDICATORS IN M DWARF K-BAND SPECTRA: TESTING NEW AND UPDATED CALIBRATIONS WITH OBSERVATIONS OF 133 SOLAR NEIGHBORHOOD M DWARFS (2011, background): “McLean et al. (2003) found that their K band water index, H2O-D, was constant for spectral types M0-M4, at which point the index decreased (due to increased H2O absorption) towards cooler spectral types.”
• YOUNG L DWARFS IDENTIFIED IN THE FIELD: A PRELIMINARY LOW-GRAVITY, OPTICAL SPECTRAL SEQUENCE FROM L0 TO L5 (2008, background): “This trend is confirmed by observed variations in the near-infrared colors and spectra of L dwarfs whose optical spectra are otherwise identical (McLean et al. 2003; Looper et al. 2008b; Burgasser et al. 2008b).”
• Subtle Signatures of Multiplicity in Late-type Dwarf Spectra: The Unresolved M8.5 + T5 Binary 2MASS J03202839–0446358 (2008, background): “However, TiO and VO bands are more similar to (but weaker than) those seen in the spectrum of VB 10, while the weak 2.2 µm Na I lines are rarely seen in L dwarf spectra (e.g., McLean et al. 2003).”
• Evidence for a co-moving sub-stellar companion of GQ Lup (2005, background): “The McLean et al. (2003) H2O−D ratio is 0.67 to 0.89 indicating L2−7 (cf. Cushing et al. 2005).”
• A Spitzer Infrared Spectrograph Spectral Sequence of M, L, and T Dwarfs (2004, background): “Its unresolved near-infrared spectrum exhibits weak CH4 absorption (McLean et al. 2003) resulting in a near-infrared spectral type of T0 (Burgasser et al. 2006) while its unresolved red-optical spectrum has been typed as L8 (Wilson et al. 2001).”
• THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS (2016, background): “5/L6 vl-g): This object serves as the archetype for extremely red L dwarfs, with an ordinary optical spectrum but a very peculiar near-IR one (Kirkpatrick et al. 2000; McLean et al. 2003).”
• DISCOVERIES FROM A NEAR-INFRARED PROPER MOTION SURVEY USING MULTI-EPOCH TWO MICRON ALL-SKY SURVEY DATA (2010, methodology): “We employed standard reductions using the IDL package, REDSPEC, as described in detail in McLean et al. (2003).”
• NEAR-INFRARED METALLICITIES, RADIAL VELOCITIES, AND SPECTRAL TYPES FOR 447 NEARBY M DWARFS (2013, methodology): “We also measured the flux ratios defined by McLean et al. (2003) and used by Cushing et al. (2005).”
• NEAR-INFRARED SPECTROSCOPY OF THE EXTRASOLAR PLANET HR 8799 b (2010, background): “There is also evidence that 2MASS J2244+2043 has a low surface gravity based on weak K i lines and FeH bands (McLean et al. 2003; Looper et al. 2008).”