New Brown Dwarfs and an Updated Initial Mass Function in Taurus

By K. Luhman. 2004

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By combining infrared photometry from the Two Micron All Sky Survey with new optical imaging and spectroscopy, I have performed a search for young low-mass stars and brown dwarfs in two regions encompassing a total area of 4 deg2 in the Taurus star-forming region (τ ~ 1 Myr). From this work I have discovered 15 new members of Taurus. In addition, I present seven new members outside of these areas from the initial stage of a survey of all of Taurus. These 22 objects exhibit spectral types of M4.5-M9.25 and masses of 0.3-0.015 M☉ according to the theoretical evolutionary models of Baraffe & Chabrier, seven of which are likely to be brown dwarfs. Emission in Hα, He I, Ca II, [O I], and [S II] and excess emission in optical and near-infrared bands among some of these objects suggest the presence of accretion, outflows, and circumstellar disks. These results add to the body of work—initiated by the first detections of brown dwarf disks by Comerón and coworkers in 1998 and Luhman in 1999—indicating that disks around young brown dwarfs are relatively common. The results from the 4 deg2 survey have been combined with previous studies of Taurus to arrive at an initial mass function (IMF) for a total area of 12.4 deg2. As in the previous IMFs for Taurus, the updated IMF peaks at a higher mass (0.8 M☉) than the mass functions in IC 348 and Orion (0.1-0.2 M☉). Meanwhile, the deficit of brown dwarfs in Taurus appears to be less significant (×1.4-1.8) than that found in earlier studies (×2) because of a slightly higher brown dwarf fraction in the new IMF for Taurus and a lower brown dwarf fraction in the new spectroscopic IMF for the Trapezium from Slesnick and coworkers. The spatial distribution of the low-mass stars and brown dwarfs discovered in the two new survey areas closely matches that of the more massive members. Thus, on the degree size scales (~3 pc) probed to date, there is no indication that brown dwarfs form through ejection.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

The Stellar Population of the Chamaeleon I Star-forming Region (2007, methodology): “Minimum Mass To date, measurements of IMFs in nearby star-forming regions have reached mass limits of ∼ 0.005-0.02 M⊙ through luminosity function modeling (Luhman et al. 2000; Hillenbrand & Carpenter 2000; Muench et al. 2002, 2003; Preibisch et al. 2003; Lucas et al. 2005) and spectroscopy (Hillenbr”
Two Regimes of Turbulent Fragmentation and the Stellar Initial Mass Function from Primordial to Present-Day Star Formation (2007, background): “The observed IMF (of multiple systems) peaks at roughly 0.2M (Chabrier 2003), with no clear evidence of a strong departure from this value in any star-forming region, with the exception of the Taurus molecular cloud complex (Luhman 2004).”
The Disk Population of the Chamaeleon I Star-forming Region (2008, methodology): “The group appears to have an age of ∼ 6 Myr and a distance of d ≃ 114 pc (Feigelson et al. 2003; Luhman 2004b).”
THE MASS DEPENDENCE BETWEEN PROTOPLANETARY DISKS AND THEIR STELLAR HOSTS (2013, methodology): “…et al. 1995; Duchêne et al. 1999; White & Ghez 2001; de Winter et al. 2001; Briceño et al. 2002; Vieira et al. 2003; Beskrovnaya & Pogodin 2004; Luhman 2004; Kraus et al. 2006; Guieu et al. 2006; Audard et al. 2007; Herczeg & Hillenbrand 2008; Luhman et al. 2009b; Duchêne et al. 2010), as…”
THE PALOMAR/KECK ADAPTIVE OPTICS SURVEY OF YOUNG SOLAR ANALOGS: EVIDENCE FOR A UNIVERSAL COMPANION MASS FUNCTION (2008, background): “0; Hillenbrand & Carpenter 2000; Slesnick et al. 2004; Luhman 2004).”
The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation (2008, background): “However, in our simulations both BDs and HBs are ejected, and hence they should be roughly co-extensive (cf. Luhman 2004; Goodwin et al. 2005; Joergens 2006b).”
ERRATUM: “THE LUMINOSITY AND MASS FUNCTIONS OF LOW-MASS STARS IN THE GALACTIC DISK. II. THE FIELD” (2010, AJ, 139, 2679) (2010, methodology): “Furthermore, if ejection is important, the spatial density of brown dwarfs should be higher near the outskirts of a cluster compared to stars, and this is not observed in Taurus (Luhman 2004a, 2006) or Chamaeleon (Joergens 2006).”
MAPPING THE SHORES OF THE BROWN DWARF DESERT. II. MULTIPLE STAR FORMATION IN TAURUS–AURIGA (2011, background): “…its observational predictions, particularly in the potential impact (or lack thereof) on the velocity and spatial distributions of star-forming regions (e.g. Luhman 2006; Kraus & Hillenbrand 2008) and the frequency and properties of disks (e.g. White & Basri 2003; Luhman 2004; Scholz et al. 2006).”
UV Excess Measures of Accretion onto Young Very Low Mass Stars and Brown Dwarfs (2008, methodology): “We adopt extinctions of ∼ 0.4, 0.1, 0.0, and 0.0 to the nonaccretors V927 Tau, MHO 7, CFHT 7, and the accretors 2M0444+2512 (Kenyon & Hartmann 1995; Briceno et al. 2002; Guieu et al. 2007; Luhman 2004).”
The Formation and Early Evolution of Low-Mass Stars and Brown Dwarfs (2012, methodology): “Although the average separation decreases with later types, a few very wide systems (> 100 AU) are present at >M6 (Luhman 2004a, Luhman et al. 2009a).”
A Spitzer Census of the IC 348 Nebula (2007, result): “We also observed a sample of 36 known late-type members of IC 348 and Taurus (Briceño et al. 1998, 2002; Luhman et al. 1998a, 2003a,b; Luhman 1999, 2004), which are listed in Figures 23-26.”
Inverse dynamical population synthesis: Constraining the initial conditions of young stellar clusters by studying their binary populations (2012, background): “Taurus was originally proposed to be deficient in lowmass stars (Briceño et al. 2002), but many brown dwarfs have since been discovered (Luhman 2004b; Guieu et al. 2006).”