Survey For Brown Dwarfs Research Articles

The NIRSPEC Brown Dwarf Spectroscopic Survey

This paper describes the status of a new 0.9 – 2.4 μm spectroscopic survey of low-mass stars and brown dwarfs. Flux-calibrated spectra of 30 objects from M6 to T8 have been obtained with a uniform spectral resolution of R=2,000. For the J-band alone, 60 objects have been observed. In addition, we have obtained the first sequence of spectra at R=20,000 (15 km/s) showing the detailed behavior of the J-band potassium doublets over the same range in spectral type. A few sources have been monitored for radial velocity variations, but none have been detected at the ±1–2 km/s level. Preliminary infrared spectral classification indices have been derived and several young brown dwarfs show clear spectral signatures of lower gravity. Our survey will be available on-line in the future.

A Large Area Survey for Brown Dwarfs in the Pleiades

We present the preliminary findings of a deep imaging survey covering 17 square degrees in the Pleiades. We have identified in excess of 300 candidate cluster members in the i, i-z diagram. The survey is complete to ~ i=22, with candidates detected as faint as i=23.

CHAOS: The Cornell High-Order Adaptive Optics Survey for Brown Dwarfs

The Cornell High-order Adaptive Optics Survey for brown dwarfs (CHAOS), currently about 90% complete, uses the Palomar Hale Telescope's adaptive optics system to survey 80 bright stars out to 13 parsecs. Using the telescope's AO Science camera, brown dwarf companions 4–200 AU can be identified using coronagraphic imaging and spectroscopic modes. We will be using monte carlo simulations to create population models consistent with the CHAOS data set.Currently, we have observed 70 systems out of a target sample of 80. Five candidate companions await follow-up observations. As of now, no systems in the target sample have shown strong evidence of having brown dwarf companions. These early results support previous speculations of a “brown dwarf desert” at orbital separations out to 200 AU.While the target sources revealed no evidence of brown dwarf companions, accompanying observations of calibration stars provided evidence of an early methane dwarf candidate around the binary system HD150451AB. Forty seven parsecs from earth, the candidate indicated a projected orbital separation of 280 AU.

Surveying the Solar Neighborhood for Brown Dwarf Companions with the ECLIPSE Discovery Mission

The proposed Eclipse Discovery mission is an optical space telescope designed to provide a thousandfold reduction in scattered light near bright stars in comparison to any Hubble Space Telescope instrument. A survey of 500 single stars within 15 pc can detect companions with absolute z magnitude of 22 at separations > 10 AU in most of the targets. Spectrophotometry of CH4 and H2O bands between 0.8-1.0 μm can be used to derive the effective temperatures of the objects. The ECLIPSE brown dwarf survey would directly measure the luminosity function of brown dwarf companions down to ~20 Jupiter masses, providing a crucial comparison with field objects.

A Survey for Low-Mass Stars and Brown Dwarfs in the Upper Scorpius OB Association

The Upper Scorpius association is the OB association nearest to the Sun (145 pc). Its young age (∼5 Myr) makes it an ideal place to search for low-mass stars and brown dwarfs, as these objects should be relatively bright. We have performed a photometric search for the low-mass members of the association, using the R, I, and Z filters. The completeness limit is I ∼ 18.5, and the saturation limit is I ∼ 13. We obtain 138 candidate members, covering nearly the entire M spectral type range. We find an excess of brown dwarf candidates over the number predicted by a Miller-Scalo initial mass function. In addition, we have performed infrared imaging and low-resolution optical spectroscopy of selected candidates. We find that the infrared observations confirm the spectral types obtained with the optical photometry. Furthermore, we find Hα in emission in 20 of the 22 objects observed spectroscopically. As Hα is an indicator of youth, we believe that these 20 objects may belong to the association. One of them, UScoCTIO 128, has a very strong and constant Hα line (equivalent width -130 Å), and its position in the color-magnitude diagram suggests that it is a brown dwarf with mass 0.02 M⊙. Confirmation of this and the other candidates will have to wait for higher resolution observations that can reveal spectroscopic mass indicators such as Li I and gravity indicators such as K I and the subordinate lines of Na I.

A six-square-degree survey for Pleiades low-mass stars and brown dwarfs

We present the results of a six-square-degree Pleiades survey in I and Z, which is photometrically complete to approximately IKP=19.2 (ICou=19.6 in the Pleiades). We remove non-cluster contamination on the basis of proper motions and infrared photometry, and present 339 candidate cluster members, 30 of which are fainter than IKP=17.5, and are thus strong brown-dwarf candidates.

A 2MASS Survey for Brown Dwarfs toward the Hyades

We present results of a search for very low mass stars and brown dwarfs toward the central region of the Hyades. Using Two Micron All Sky Survey (2MASS) near-infrared and Second Palomar Sky Survey (POSS II) optical photometry, we select candidates corresponding to spectral types M8–L4 at the distance of the Hyades. Spectroscopic follow-up data indicate that none are cluster members. The lack of members in the mass range 0.08 M⊙ < M < 0.06 M⊙ is consistent with evidence that this 600 Myr–old cluster is deficient in very low mass objects. Three of our objects are of spectral type M8, with surface gravity–sensitive features intermediate between dwarfs and giants. We interpret these objects as background brown dwarfs, perhaps associated with the Taurus star formation region.

A new population of brown dwarfs

In this paper we report the first results from a survey for low-mass stars and brown dwarfs, based on a photographic stack of around 100 Schmidt plates. This survey extends photographic searches by about 2 mag, and covers an area of 25 deg2. Some 30 faint objects with large R−I colours were selected for further study, and were found to have very strong molecular absorption in their spectra, but only moderately red infrared colours. Five of these stars were selected for a parallax programme; three of these were found to be at a distance of around 45 pc, implying a very low luminosity. On the basis of their luminosity alone it is clear that these stars are field brown dwarfs, and we discuss their likely evolutionary status in the context of current models of low-mass stellar evolution.

A Southern Sky Survey of Low Mass Stars and Brown Dwarfs

AbstractWe are conducting a survey of the southern sky to study the properties of the lowest mass stars and the sub-stellar brown dwarf population thought to exist at masses below 0.08 M⊙. The survey makes use of plates from the UK and ESO Schmidt telescopes, using the new SuperCOSMOS plate measuring machine at Edinburgh to provide a catalogue of photographic BRI colours and proper motion measurements. Candidates are selected by extreme R–I colour (&gt; 2.5) to a plate-limited magnitude of I ≈ 19.0 and R ≈ 21.0. The size of the survey is only limited by the progress of the UK Schmidt I band survey and the availability of photometric data for calibration of SuperCOSMOS measurements. It is anticipated that the survey will form part of a multi-colour proper motion database of southern sky objects.