P. S. Chen

Ultra-cool dwarfs: new discoveries, proper motions, and improved spectral typing from SDSS and 2MASS photometric colors

Aims. We try to identify ultra-cool dwarfs from the seventh Data Release of the Sloan Digital Sky Survey (SDSS DR7) with SDSS i-z and r-z colors. We also obtain proper motion data from SDSS, 2MASS, and UKIDSS and improve spectral typing from SDSS and 2MASS photometric colors. Methods. We selected ultra-cool dwarf candidates from the SDSS DR7 with new photometric selection criteria, which are based on a parameterization study of known L and T dwarfs. The objects are then cross-identified with the Two Micron All Sky Survey and the Fourth Data Release of the UKIRT Infrared Deep Sky Survey (UKIDSS DR4). We derive proper motion constraints by combining SDSS, 2MASS, and UKIDSS positional information. In this way we are able to assess, to some extent, the credence of our sample using a multi epoch approach, which complements spectroscopic confirmation. Some of the proper motions are affected by short baselines, but, as a general tool, this method offers great potential to confirm faint L dwarfs as UKIDSS coverage increases. In addition we derive updated color-spectral type relations for L and T dwarfs with SDSS and 2MASS magnitudes. Results. We present 59 new nearby M and L dwarfs selected from the imaging catalog of the SDSS DR7, including proper motions and spectral types calculated from the updated color-spectral type relations. and obtain proper motions from SDSS, 2MASS, and UKIDSS for all of our objects.

Molecular and dust features of 29 SiC carbon AGB stars

We have reduced and analyzed the Infrared Space Observatory (ISO) Short-Wavelength Spectrometer (SWS) spectra of 29 infrared carbon stars with a silicon carbide feature at 11.30 mum, 17 of which have not been previously published. Absorption or emission features of C-2, HCN, C2H2, C-3 and silicon carbide (SiC) have been identified in all 17 unpublished carbon stars. In addition, two unidentified absorption features at 3.50 and 3.65 mum are listed for the first time in this paper. We classify these 29 carbon stars into groups A, B, C and D according to the shapes of their spectral energy distribution, and this classification seems to show an evolutionary sequence of carbon stars with an SiC feature. Moreover we have found the following results for the different groups: on average, the relative integrated flux of the 3.05 mum C2H2+HCN absorption feature increases gradually from group A to B and C; that of the 5.20 mum C-3 absorption feature becomes gradually weaker from group A to B and C; that of the 11.30 mum SiC emission feature increases gradually from group A to B and C but weakens in group D; and in contrast, that of the 13.70 mum C2H2 absorption feature weakens gradually from group A to B and C but becomes stronger in group D. We suggest that the evolution of the IR spectra of carbon stars along the sequence A to D is a result of the following phenomena: as the near-IR black-body temperature (T-nir) decreases, the circumstellar envelope becomes thicker; also the effective temperature (T-eff) of the photosphere of the central star decreases gradually and the C/O ratio increases from A to B.

Infrared Study of J-Type Carbon Stars Based on Infrared Astronomical Satellite, Two Micron All Sky Survey, and Infrared Space Observatory Data

collected 113 J-type carbon stars from the published literature. Observations from 2MASS, IRAS, and ISO show that, except for silicate carbon stars in the J-type carbon star domain, the infrared properties of the other J-type carbon stars are quite similar to those of ordinary carbon stars. The above results imply that the chemical peculiarity of enhanced C-13 for J-type carbon stars is not reflected in the infrared region. In addition, the possible evolutionary scenario and binarity for J-type carbon stars are also discussed.

Two Micron All Sky Survey, Infrared Astronomical Satellite, and Midcourse Space Experiment Color Properties of Intrinsic and Extrinsic S Stars

We attempt to select new candidate intrinsic and extrinsic S stars in the General Catalogue of Galactic S Stars (GCGSS) by combining data from the Two Micron All Sky Survey, the Infrared Astronomical Satellite, and the Midcourse Space Experiment. Catalog entries are cross-identified, yielding 528 objects, out of which 29 are known extrinsic S stars and 31 are known intrinsic S stars. Their color-color diagrams, (H - [12])-(K [12]) and ( K - [12])-(J - [25]), are drawn and used to identify a new sample of 147 extrinsic and 256 intrinsic S star candidates, while the nature of 65 stars remains identified. We infer that about 38% +/- 10% of the GCGSS objects are of extrinsic type. Moreover, we think that colors such as J - [25] can be used to split off the two categories of S stars, while single colors are not appropriate. The color-color diagrams, such as (H - [12])-(K - [12]) and (K - [12])-(J - [25]), are proven to be powerful tools for distinguishing the two kinds of S stars.

Newly identified infrared carbon stars from the IRAS low-resolution spectra

We report new identifications of 63 infrared carbon stars and 24 possible candidates based on the presence of the SiC emission feature at 11.2 mum in their IRAS low-resolution spectra and on their infrared colors. The IRAS spectra of the newly identified carbon stars are presented.

Photometric study of galaxies with OH megamasers in the infrared

OH megamasers are the most luminous masers in the universe. The total of 109 OH megamaser (OHM) galaxies known so far have been collected, and cross-identifications of those OHM galaxies with Two Micron All Sky Survey (2MASS) sources are made in this paper. Using 2MASS and IRAS data, the infrared properties of OHM-detected and nondetected sources are compared. It is shown that the main difference between those two kinds of sources is the infrared color from 25 to 60 mu m. Statistically, the OHM-detected sources have redder colors and steeper spectral indices in the 25-60 mu m region than the nondetected sources. In addition, considering the spectral types, the properties of the OHM galaxies in the near-infrared and far-infrared are discussed. It is found that Seyfert 1 and Seyfert 2 sources with hidden broad-line regions (BLRs) have redder colors and steeper spectral indices than other sources, including LINER, composite spectrum nucleus, and H II sources in the near-infrared region, whereas the latter have redder colors and steeper spectral indices than the Seyfert 1 and Seyfert 2 sources with hidden BLRs in the far-infrared. It is also found that almost all sources either with or without an identified spectral type show a starburst-dominated feature in the far-infrared, while a considerable number of sources, in particular Seyfert 1 and Seyfert 2 sources with hidden BLRs, show an active galactic nucleus-dominated feature in the near-infrared. Furthermore, as far-infrared radiation at 35 and 53 mu m is likely responsible for the OH maser pumping in OHM galaxies, the pumping efficiencies in the infrared are also analyzed in this paper. It is found that, statistically, the pumping efficiencies increase with far-infrared color. It is also found that, statistically, the OH peak fluxes are not proportional to the related infrared fluxes at either 35 or 53 mu m. This result implies that the pump lines are optically thin and the pump sources are unsaturated.

Analysis of ISO SWS01 spectra of S stars

The Infrared Space Observatory (ISO) Short-Wavelength Spectrometer (SWS01) plays an important role in studying properties of S stars. We reduce and analyze the SWS01 spectra of 17 S stars, and identify the candidate carriers of molecular absorption features. The ISO Spectral Analysis Package (ISAP) developed by the LWS and SWS Instrument Teams and Data Centers is used to process and analyze the SWS01 spectra of 17 S stars. The ISO archives of 17 S stars are obtained from the ISO database. Of 17 S stars, two stars are extrinsic S stars, the others are intrinsic S stars. The 15 intrinsic S stars can be divided into three groups (6 stars for Group I, 7 stars for Group II, and 2 stars for Group III) according to their Infrared Astronomical Satellite (IRAS) low-resolution spectra (LRS) and dust mass-loss rate. M-dust, where. M-dust increases from Group I to II and III gradually. 17 S stars show the following properties: 1. two extrinsic S stars and 15 intrinsic S stars among different groups have different infrared properties; 2. two extrinsic S stars and 6 intrinsic S stars in Group I have similar ISO SWS01 spectra and their continua can be approximately described by a single blackbody representing the stellar photosphere, while some intrinsic S stars in Group I have 60 mu m infrared excess; 3. for intrinsic S stars in Groups I, II, and III, their continua peak shifts toward longer wavelength from Groups I to II to III; 4. S stars in Groups II and III show obvious dust emission features in which the similar to 10 mu m dust features seem to display two different shapes. Moreover, two S stars (IRAS 00192-2020 & IRAS 15492 + 4837) present the 13 mu m feature; 5. molecules H2O, CO, and CO2 greatly affect the ISO SWS01 spectra of S stars. It is noted that the absorption features of molecules CS and HCN usually thought to exist only in C stars may appear in the S stars.

Infrared Photometric Study for the IRAS 1 Jy Sample of Ultraluminous Infrared Galaxies

The Two Micron All Sky Survey observation of the IRAS 1 Jy sample of ultraluminous infrared galaxies (ULIRGs) is presented in this paper. Together with the IRAS photometric data, the properties and energy sources of the IRAS 1 Jy sample of ULIRGs in the near- and far-infrared are discussed. It is shown that most sources, not only Seyfert galaxies but also H II and LINER galaxies, have a radiation mechanism with a power-law continuum in the near- infrared. All Seyfert 1 sources and some Seyfert 2 sources with hidden broad-line regions (BLRs) have much redder colors and steeper spectral indices in the near- infrared, indicative of an extremely strong energy source from the central active galactic nucleus. Almost all sources have thermal radiation indicative of starburst domination in the IRAS region; in particular, all Seyfert 1 sources and many Seyfert 2 sources with hidden BLRs have lower [25]-[60] colors, indicative of a flatter spectral continuum and a rather warm color temperature in the 25-60 mu m region. However, all kinds of sources have similar [60]-[100] color distributions, indicative of similar energy sources from the enhanced heating in active star-forming regions and very cold material and also indicative of the quite small influence from the central activity in the 60-100 mu m region. In addition, all Seyfert 1 sources and some Seyfert 2 sources with hidden BLRs have much larger absolute magnitudes in the K band compared with other sources. The results presented in this paper may further help us to understand the physical properties of ULIRGs.

A study of the EB-type eclipsing binary GR Tauri with mass transfer

In this paper, new CCD BV light curves of the EB-type eclipsing binary GR Tau, which were obtained in 1999, are analyzed by means of the Wilson-Devinney program. The photometric solution of this system is obtained, and its absolute parameters are also derived. Our study has demonstrated that GR Tau is a near-contact binary system with an almost-contact semidetached configuration in which the primary fills its Roche lobe, and both components are main-sequence stars. The asymmetric shape of the light curves can be explained by a hot spot on the surface of the secondary, which is created by the mass transfer from the primary to the secondary. GR Tau belongs to the V 1010 Oph subclass of near-contact binaries, and is a good example of a system in the broken-contact phase predicted by the TRO theory.

A CATALOG OF GALACTIC INFRARED CARBON STARS

We collected almost all of the Galactic infrared carbon stars (IRCSs) from literature published up to the present to organize a catalog of 974 Galactic IRCSs in this paper. Some of their photometric properties in the near-, mid-, and far-infrared are discussed.