Discovery of a Second L Subdwarf in the Two Micron All Sky Survey

I report the discovery of the second L subdwarf identified in the Two Micron All Sky Survey, 2MASS J16262034+3925190. This high proper motion object (mu = 1.27+/-0.03 "/yr) exhibits near-infrared spectral features indicative of a subsolar metallicity L dwarf, including strong metal hydride and H2O absorption bands, pressure-broadened alkali lines, and blue near-infrared colors caused by enhanced collision-induced H2 absorption. This object is of later type than any of the known M subdwarfs, but does not appear to be as cool as the apparently late-type sdL 2MASS 0532+8246. The radial velocity (Vrad = -260+/-35 km/s) and estimated tangential velocity (Vtan ~ 90-210 km/s) of 2MASS 1626+3925 indicate membership in the Galactic halo, and this source is likely near or below the hydrogen burning minimum mass for a metal-poor star. L subdwarfs such as 2MASS 1626+3925 are useful probes of gas and condensate chemistry in low-temperature stellar and brown dwarf atmospheres, but more examples are needed to study these objects as a population as well as to define a rigorous classification scheme.Comment: 11 pages, 3 figures, accepted for publication ApJ Letters, v. 614 October 200

The Inner Galaxy resolved at IJK using DENIS data

We present the analysis of three colour optical/near-infrared images, in IJK, taken for the DENIS project. The region considered covers 17.4 square deg and lies within |l|<5 deg, |b|<1.5 deg. The adopted methods for deriving photometry and astrometry in these crowded images, together with an analysis of the deficiencies nevertheless remaining, are presented. The numbers of objects extracted in I,J and K are 748000, 851000 and 659000 respectively, to magnitude limits of 17,15 and 13. 80% completeness levels typically fall at magnitudes 16, 13 and 10 respectively, fainter by about 2 magnitudes than the usual DENIS limits due to the crowded nature of these fields. A simple model to describe the disk contribution to the number counts is constructed, and parameters for the dust layer derived. We find that a formal fit of parameters for the dust plane, from these data in limited directions, gives a scalelength and scaleheight of 3.4+-1.0 kpc and 40+-5 pc respectively, and a solar position 14.0+-2.5 pc below the plane. This latter value is likely to be affected by localised dust asymmetries. We convolve a detailed model of the systematic and random errors in the photometry with a simple model of the Galactic disk and dust distribution, to simulate expected colour-magnitude diagrams. These are in good agreement with the observed diagrams, allowing us to isolate those stars from the inner disk and bulge. After correcting for local dust-induced asymmetries, we find evidence for longitude-dependent asymmetries in the distant J and K sources, consistent with the general predictions of some Galactic bar models. We consider complementary L-band observations in a second paper.Comment: 14 pages, 33 figures, LaTeX, MNRAS accepte

The Schizophrenic Spectrum of LSR 1610-0040: a Peculiar M Dwarf/Subdwarf

We present a moderate resolution (R=2000), 0.8-4.1 micron spectrum of LSR 1610-0040, a high proper motion star classified as an early-type L subdwarf by Lepine and collaborators based on its red-optical spectrum. The near-infrared spectrum of LSR 1610-0040 does not fit into the (tentative) M/L subdwarf sequence but rather exhibits a mix of characteristics found in the spectra of both M dwarfs and M subdwarfs. In particular, the near-infrared spectrum exhibits a Na I doublet and CO overtone bandheads in the K band, and Al I and K I lines and an FeH bandhead in the H band, all of which have strengths more typical of field M dwarfs. Furthermore the spectrum of Gl 406 (M6 V) provides a reasonably good match to the 0.6-4.1 micron spectral energy distribution of LSR 1610. Nevertheless the near-infrared spectrum of LSR 1610 also exhibits features common to the spectra of M subdwarfs including a strong Ti I multiplet centered at ~0.97 microns, a weak VO band at ~1.06 microns, and possible collision-induced H_2 absorption in the H and K bands. We discuss a number of possible explanations for the appearance of the red-optical and near-infrared spectrum of LSR 1610-0040. Although we are unable to definitively classify LSR 1610-0040, the preponderance of evidence suggests that it is a mildly metal-poor M dwarf. Finally, we tentatively identify a new band of TiO at ~0.93 microns in the spectra of M dwarfs.Comment: Accepted for publication in the Astronomical Journa

Extinctions at 7um and 15um from the ISOGAL survey

The extinction laws at 7um and 15um are derived for more than 120 sightlines in the inner Galactic plane based on the ISOGAL survey data and the near-infrared data from DENIS and 2MASS. The tracers are the ISOGAL point sources with [7]-[15]<0.4 which are RGB tip stars or early AGB stars with moderate mass loss. They have well-defined intrinsic color indices (J-Ks)_0, (Ks-[7])_0 and (Ks-[15])_0. By a linear fitting of the observed color indices Ks-[7] and Ks-[15] to the observed J-Ks, we obtain the ratio between the E(Ks-[7]) and E(Ks-[15]) color excesses and E(J-Ks). We infer the selective extinctions at 7 and 15um in terms of the near-infrared extinction in the Ks band. The distribution of the derived extinctions around 7 micron (A_7) is well represented by a Gaussian function, with the peak at about 0.47A_Ks and ranging from 0.33 to 0.55A_Ks (using the near-infrared extinctions of Rieke & Lebovsky 1985). There is some evidence that A_7/A_Ks may vary significantly depending on the line of sight. The derived selective extinction at 15um suffers uncertainty mainly from the dispersion in the intrinsic color index (Ks-[15])_0 which is affected by dust emission from mass-losing AGB stars. The peak value of A_15 is around 0.40A_Ks.Comment: 21 pages, 6 figures, accepted for publication in Astronomy and Astrophysic

Resolved Spectroscopy of M Dwarf/L Dwarf Binaries. II. 2MASS J 17072343-0558249AB

We present IRTF SpeX observations of the M/L binary system 2MASS J17072343-0558249. SpeX imaging resolves the system into a 1"01+/-0.17 visual binary in which both components have red near infrared colors. Resolved low-resolution (R~150) 0.8-2.5 micron spectroscopy reveals strong H2O, CO and FeH bands and alkali lines in the spectra of both components, characteristic of late-type M and L dwarfs. A comparison to a sample of late-type field dwarf spectra indicates spectral types M9 and L3. Despite the small proper motion of the system (0"100+/-0"009 yr^{-1}), imaging observations over 2.5 yr provide strong evidence that the two components share common proper motion. Physical association is also likely due to the small spatial volume occupied by the two components (based on spectrophotometric distances estimates of 15+/-1 pc) as compared to the relatively low spatial density of low mass field stars. The projected separation of the system is 15+/-3 AU, similar to other late-type M and L binaries. Assuming a system age of 0.5-5 Gyr, we estimate the masses of the binary components to be 0.072-0.083 and 0.064-0.077 M_sun, with an orbital period of roughly 150-300 yr. While this is nominally too long a baseline for astrometric mass measurements, the proximity and relatively wide angular separation of the 2MASS J1707-0558AB pair makes it an ideal system for studying the M dwarf/L dwarf transition at a fixed age and metallicity

The 2MASS Wide-Field T Dwarf Search. II. Discovery of Three T Dwarfs in the Southern Hemisphere

We present the discovery of three new Southern Hemisphere T dwarfs identified in the Two Micron All Sky Survey. These objects, 2MASS 0348-6022, 2MASS 0516-0445, and 2MASS 2228-4310, have classifications T7, T5.5, and T6.5, respectively. Using linear absolute magnitude/spectral type relations derived from T dwarfs with measured parallaxes, we estimate spectrophotometric distances for these discoveries; the closest, 2MASS 0348-6022, is likely within 10 pc of the Sun. Proper motions and estimated tangential velocities are consistent with membership in the Galactic disk population. We also list Southern Hemisphere T dwarf candidates that were either not found in subsequent near-infrared imaging observations and are most likely uncatalogued minor planets, or have near-infrared spectra consistent with background stars.Comment: 12 pages including 4 figures (one as jpeg), accepted to A

DENIS Observations of Multibeam Galaxies in the Zone of Avoidance

Roughly 25% of the optical extragalactic sky is obscured by the dust and stars of our Milky Way. Dynamically important structures might still lie hidden in this zone. Various surveys are presently being employed to uncover the galaxy distribution in the Zone of Avoidance (ZOA) but all suffer from (different) limitations and selection effects. We illustrate the promise of using a multi-wavelength approach for extragalactic large-scale studies behind the ZOA, i.e. a combination of three surveys -- optical, systematic blind HI and near-infrared (NIR), which will allow the mapping of the peculiar velocity field in the ZOA through the NIR Tully-Fisher relation. In particular, we present here the results of cross-identifying HI-detected galaxies with the DENIS NIR survey, and the use of NIR colours to determine foreground extinctions.Comment: Accepted for publication in PASA. Proceedings of workshop "HI in the Local Universe, II", held in Melbourne, Sept. 1998. 9 pages, LaTeX2e, 2 encapsulated PS figures, 3 JPEG figures, Full resolution figures 2, 3 and 4 and full resolution paper are at ftp://ftp.iap.fr/pub/from_users/gam/PAPERS/HICONF

First DENIS I-band extragalactic catalog

This paper presents the first I-band photometric catalog of the brightest galaxies extracted from the Deep Near Infrared Survey of the Southern Sky (DENIS) An automatic galaxy recognition program has been developed to build this provisional catalog. The method is based on a discriminating analysis. The most discriminant parameter to separate galaxies from stars is proved to be the peak intensity of an object divided by its array. Its efficiency is better than 99%. The nominal accuracy for galaxy coordinates calculated with the Guide Star Catalog is about 6 arcseconds. The cross-identification with galaxies available in the Lyon-Meudon Extragalactic DAtabase (LEDA) allows a calibraton of the I-band photometry with the sample of Mathewson et Al. Thus, the catalog contains total I-band magnitude, isophotal diameter, axis ratio, position angle and a rough estimate of the morphological type code for 20260 galaxies. The internal completeness of this catalog reaches magnitude $I_{lim}=14.5$, with a photometric accuracy of $\sim 0.18m$. 25% of the Southern sky has been processed in this study. This quick look analysis allows us to start a radio and spectrographic follow-up long before the end of the survey.Comment: 13 pages, 17 figures, to appear A&A Supl.