Carlos A. O. Torres

The Pico dos Dias Survey Starburst Galaxies

We discuss the nature of the galaxies found in the Pico dos Dias Survey (PDS) for young stellar objects. The PDS galaxies were selected from the IRAS Point Source catalog. They have flux density of moderate or high quality at 12, 25, and 60 ?m and spectral indices in the ranges -3.00 ? ?(25, 12) ? + 0.35 and -2.50 ? ?(60, 25) ? +0.85. These criteria allowed the detection of 382 galaxies, which are a mixture of starburst and Seyfert galaxies. Most of the PDS Seyfert galaxies are included in the catalog of warm IRAS sources by de Grijp et al. The remaining galaxies constitute a homogeneous sample of luminous [log F (LB/L?) = 9.9 ? 0.4] starburst galaxies, 67% of which were not recognized as such before. The starburst nature of the PDS galaxies is established by comparing their LIR/LB ratios and IRAS colors with a sample of emission-line galaxies from the literature already classified as starburst galaxies. The starburst galaxies show an excess of FIR luminosity, and their IRAS colors are significantly different from those of Seyfert galaxies-99% of the starburst galaxies in our sample have a spectral index ?(60, 25) -2.5. This color cutoff also marks a change in the dominant morphologies of the galaxies: the normal IRAS galaxies are preferentially late-type spirals (Sb and later), while the starbursts are more numerous among early-type spirals (earlier than Sbc). This preference of starbursts for early-type spirals is not new, but a trait of the massive starburst nucleus galaxies (Coziol et al.). As in other starburst nucleus galaxy samples, the PDS starbursts show no preference for barred galaxies. No difference is found between the starbursts detected in the FIR and those detected on the basis of UV excess. The PDS starburst galaxies represent the FIR luminous branch of the UV-bright starburst nucleus galaxies, with mean FIR luminosity log (LIR/L?) = 10.3 ? 0.5 and redshifts smaller than 0.1. They form a complete sample limited in flux in the FIR at 2 ? 10-10 ergs cm-2 s-1.

Discovery of a Luminous Quasar in the Nearby Universe

In the course of the Pico dos Dias survey (PDS), we identified the stellar-like object PDS 456 at coordinates a 5 17 h 28 m 19 s d 52 147159550 (epoch 2000), with a relatively nearby (z 5 0.184) and bright (B 5 14.69) quasar. Its position at Galactic coordinates l 5 107 b 51 117 .2, near the bulge of the Galaxy, may explain why it was not detected before. The optical spectrum of PDS 456 is typical of a luminous quasar, showing a broad (FWHM » 4000 km s 21 )H bline, very intense Fe ii lines, and a weak [O iii] l5007 line. PDS 456 is associated to the infrared source IRAS 1725421413 with a 60 mm infrared luminosity L60 5 3.8 # 10 45 ergs s 21 . The relatively flat slopes in the infrared [ a(25, 60) 52 0.33 and a(12, 25) 52 0.78] and a flat power index in the optical (Fn / n 20.72 ) may indicate a low dust content. A good match between the position of PDS 456 and the position of the X-ray source RXS J172819.32141600 implies an X-ray luminosity LX 5 2.8 # 10 44 ergs s 21 . The good correlation between the strength of the emission lines in the optical and the X-ray luminosity, as well as the steep optical to X-ray index estimated (aOX 52 1.64), suggests that PDS 456 is radio quiet. A radio survey previously performed in this region yields an upper limit for radio power at about 5 GHz of approximately 2.6 # 10 30 ergs 21 Hz 21 . We estimate the Galactic reddening in this line of sight to be AB . 2.0, implying an absolute magnitude MB 52 26.7 (using H0 5 75 km s 21 Mpc 21 and q0 5 0). In the optical, PDS 456 is therefore 1.3 times more luminous than 3C 273 and the most luminous quasar in the nearby (z • 0.3) universe. Subject headings: infrared: general — quasars: individual (PDS 456, IRAS 17254 21413) — X-rays: galaxies

The triple system HIP 96515: a low-mass eclipsing binary with a DB white dwarf companion

Context. HIP 96515 A is a double-lined spectroscopic binary included in the SACY catalog as a potential young star. It has a visual companion (CCDM 19371-5134 B, HIP 96515 B) at 8. �� 6. If bound to the primary, the optical and infrared colors of this wide companion are consistent with those of a white dwarf. Aims. We attempt to characterize the system HIP 96515 A&B by studying each of its components. Methods. We analyzed spectroscopic and photometric observations of HIP 96515 A and its visual companion, HIP 96515 B. To confirm the system as a common proper-motion pair, we analyzed the astrometry of the components using high-angular resolution infrared observations obtained within a time span of two years, and archival astrometry. Results. The high-resolution optical spectrum of HIP 96515 A was used to derive a mass ratio, M2/M1, close to 0.9. The optical lightcurve of HIP 96515 A shows periodic variations with Porbital = 2.3456 days, revealing that HIP 96515 A is an eclipsing binary with preliminary orbital parameters of i = 89. ◦ 0 ± 0. ◦ 2, and M 1

Photometric and spectroscopic analysis of the stellar association AB Doradus

We present the stellar parameters and lithium abundance for 23 stars of the young stellar association AB Doradus, determined by photometry and spectroscopy. The photometric data was obtained at OPD/LNA and/or from the literature and the spectroscopic data was obtained at La silla/ESO and at OPD/LNA. The parameters were determined using photometric calibrations, line ratios, curves of growth and spectral synthesis. Our results confirm that the selected stars are probably association members, showing an uniform metallicity and lithium depletion consistent with 50 Myears

Lithium abundances in southern associations containing young stars

In a recent paper, da Silva et al. (2009), we report results of Li abundance analysis for nine young stellar associations, defined in Torres et al. (2008), from a high-resolution optical spectroscopic survey searching for associations containing young stars (SACY), among optical counterparts of ROSAT All-Sky X-ray sources in the Southern Hemisphere. They have applied a convergence method in the (UVW) velocity space and have determined nine nearby young associations in the sample. As they are young and with different ages, those associations form an interesting laboratory to test the Li depletion theory, as a function of the star age.

The Li Abundance and the Age of AB Dor Association

In a recent paper (Torres et al. 2006) we report the results from a highresolution optical spectroscopic survey searching for associations containing young stars (SACY), among optical counterparts of ROSAT All-Sky X-ray sources in the Southern Hemisphere. We have applied a convergence method in the (UVW) velocity space and have found several nearby young associations in the sample. As they are young and with different ages, those associations form an interesting laboratory to test the Li depletion theory, as a function of the star age. We present here our determination of Li abundance for two of them, the β Pic and AB Dor Associations.

The Atmosphere of a Probably Very Young by Dra-Type Flare Star

The flare star Gliese 182 (dM0.5e) seems to be only known single BY Dra type that presents Li in its atmosphere. This characteristic and others, principally activity, and high rotation, indicate that probably this is a very young object. We analyse in this work the possibility to interpret with a single typical model for a dMe atmosphere, some observed lines of Gliese 182 and to predict others. The lines belong to the following atoms; Li I, H I, He I, He II, C I, C II. A relatively good agreement exists only for neutral lines but not for ionized lines. The upper chromosphere and transition region must be studied in more detail. Some comparison are made with the UV observations of the double star BY Dra. Empirical relatively high X-ray fluxes are predicted for both stars. The Li abundance of Gliese 182 is confirmed to be similar to that of the interstellar medium.