Germano R. Quast

Investigation of 131 Herbig Ae/Be Candidate Stars*

We present a new catalog of 108 Herbig Ae/Be candidate stars identified in the Pico dos Dias Survey, together with 19 previously known candidates and four objects selected from the IRAS Faint Source Catalog. These 131 stars were observed with low- and/or medium-resolution spectroscopy, and we complement these data with high-resolution spectra of 39 stars. The objects present a great variety of Hα line profiles and were separated according to them. Our study suggests that most of the time a Herbig Ae/Be star will present a double peak Hα line profile. Correlations among different physical parameters, such as spectral type and v sin i with Hα line profiles were searched. We found no correlation among Hα line profiles and spectral type or v sin i except for stars with P Cygni profiles, where there is a correlation with v sin i. We also use preliminary spectral energy distributions to seek for any influence of the circumstellar medium in the Hα line profiles. The presence of [O I] and [S II] forbidden lines is used together with the Hα line profiles and these preliminary spectral energy distributions to discuss the circumstellar environment of the Herbig Ae/Be candidates. The distribution of the detected [O I] and [S II] forbidden lines among different spectral types points to a significantly higher occurrence of these lines among B stars, whereas the distribution among different Hα profile types indicates that forbidden lines are evenly distributed among each Hα line-profile type. Combining the distance estimates of the Herbig candidates with the knowledge of the interstellar medium distribution, we have found that 84 candidates can be associated with some of the more conspicuous SFRs, being in the right direction and at a compatible distance. As a further means of checking the properties of the HAeBe candidates, as well as their present evolutionary status, the derived luminosities and effective temperatures of the stars with possible association to the star-forming regions and/or Hipparcos distances were plotted together with a set of pre–main-sequence evolutionary tracks on an HR diagram. A set of 14 stars were found out of their expected positions in the HR diagram.

Search for associations containing young stars (SACY) - III. Ages and Li abundances

Context. Our study is a follow-up of the SACY project, an extended high spectral resolution survey of more than two thousand optical counterparts of X-ray sources in the Southern Hemisphere targeted to search for young nearby associations. Nine associations have either been newly identified, or had their member list better defined. Groups belonging to the Sco-Cen-Oph complex are not considered in the present study. Aims. These nine associations, with ages between about 6Myr and 70Myr, form an excellent sample to study the Li depletion in the pre-main sequence(PMS) evolution. In the present paper we investigate the use of Li abundances as an independent clock to constrain the PMS evolution. Methods. Using our measurements of the equivalent widths of the Li resonance line and assuming fixed metallicities and microturbulence, we have calculated the LTE Li abundances for 376 members of different young associations. In addition we considered the effects of their projected stellar rotation. Results. We present the Li depletion as function of age in the first hundred million years for the first time for the most extended sample of Li abundances in young stellar associations. Conclusions. A clear Li depletion can be measured in the temperature range from 5000 K to 3500 K for the age span covered by the nine associations studied in this paper. The age sequence based on the Li-clock agrees well with the isochronal ages, ǫCha association being the only possible exception. The lithium depletion patterns for the associations presented here resemble those of the young open clusters with similar ages, strengthening the notion that the members proposed for these loose young associations have indeed a common physical origin. The observed scatter in the Li abundances hampers the use of Li to determine reliable ages for individual stars. For velocities above 20kms 1 rotation seems to play an important role inhibiting the Li depletion.

Discovery of new isolated T Tauri stars

Two new T Tauri stars (TTSs) have been discovered in the neighborhood of the isolated, strong H-alpha emitting, TTS (CTTS) TW Hya (b = 23 deg). The first object is a visual binary star formed by two CTTSs separated by 1.5 arcsec (b = 21 deg). The second object may be a weakly H-alpha emitting TTS (b = 28 deg). The high latitudes of the stars indicate that their distances cannot be very large. All these TTSs have similar radial velocities, suggesting the possibility that they are kinematically related. As the nearest cloud is quite far from this group of stars, star formation in situ must be considered. 20 refs.

A New Association of Post-T Tauri Stars near the Sun*

Observing ROSAT sources in an area 20° × 25° centered at the high-latitude (b = -59°) active star ER Eri, we found evidences for a nearby association, that we call the Horologium association (HorA), formed by at least 10 very young stars, some of them being bona fide post–T Tauri stars. We suggest other six stars as possible members of this proposed association. We examine several requirements that characterize a young stellar association. Although no one of them, isolated, gives an undisputed prove of the existence of the HorA, all together practically create a strong evidence for it. In fact, the Li line intensities are between those of the older classical T Tauri stars and the ones of the Local Association stars. The space velocity components of the HorA relative to the Sun (U = -9.5 ± 1.0, V = -20.9 ± 1.1, W = -2.1 ± 1.9) are not far from those of the Local Association, so that it could be one of its last episodes of star formation. In this region of the sky there are some hotter and non–X-ray active stars, with similar space velocities, that could be the massive members of the HorA, among them, the nearby Be star Achernar. The maximum of the mass distribution function of its probable members is around 0.7–0.9 M☉. We estimate its distance as ~60 pc and its size as ~50 pc. If spherical, this size would be larger than the surveyed area, and many other members could have been missed. ER Eri itself was found to be not a member, but a background RS CVn–like system. We also observed three control regions, two at northern and southern Galactic latitudes and a third one in the known TW Hya association (TWA), and the properties and distribution of their young stars strengthen the reality of the HorA. Contrary to the TWA, the only known binaries in the HorA are two very wide systems. The HorA is much more isolated from clouds and older (~30 Myr) than the TWA and could give some clues about the lifetime of the disks around T Tauri stars. Actually, none of the proposed members is an IRAS source indicating an advanced stage of the evolution of their primitive accreting disks.

Search for associations containing young stars (SACY) - V. Is multiplicity universal? Tight multiple systems

Context. Dynamically undisrupted, young populations of stars are crucial in studying the role of multiplicity in relation to star formation. Loose nearby associations provide us with a great sample of close (<150 pc) pre-main sequence (PMS) stars across the very important age range (≈5-70 Myr) to conduct such research. Aims. We characterize the short period multiplicity fraction of the search for associations containing young stars (SACY) sample, accounting for any identifiable bias in our techniques and present the role of multiplicity fractions of the SACY sample in the context of star formation. Methods. Using the cross-correlation technique we identified double-lined and triple-lined spectroscopic systems (SB2/SB3s), in addition to this we computed radial velocity (RV) values for our subsample of SACY targets using several epochs of fiber-fed extended range optical spectrograph (FEROS) and ultraviolet and visual echelle spectrograph (UVES) data. These values were used to revise the membership of each association that was then combined with archival data to determine significant RV variations across different data epochs characteristic of multiplicity; single-lined multiple systems (SB1). Results. We identified seven new multiple systems (SB1s: 5, SB2s: 2). We find no significant difference between the short period multiplicity fraction (Fm) of the SACY sample and that of close star-forming regions (≈1-2 Myr) and the field (Fm ≤10%). These are seen both as a function of age and as a function of primary mass, M1, in the ranges P [1:200 day] and M2 [0.08 M -M1], respectively. Conclusions. Our results are consistent with the picture of universal star formation, when compared to the field and close star-forming regions (SFRs). We comment on the implications of the relationship between increasing multiplicity fraction with the primary mass within the close companion range in relation to star formation.

A search for T-Tauri stars based on the IRAS Point Source Catalog

T-Tauri stars represent the class of pre-main sequence stars which evolve to solar-type main-sequence stars. It is of interest to investigate the occurrence of circumstellar disks, which are believed to give origin to planets at this stage of evolution.

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

Search for associations containing young stars (SACY) VI. Is multiplicity universal? Stellar multiplicity in the range 3-1000 au from adaptive-optics observations ?;??;???

Context. Young loose nearby associations are unique samples of close (<150 pc), young (approx 5-100 Myr) pre-main sequence (PMS) stars. A significant number of members of these associations have been identified in the SACY collaboration. We can use the proximity and youth of these members to investigate key ingredients in star formation processes, such as multiplicity. Aims. We present the statistics of identified multiple systems from 113 confirmed SACY members. We derive multiplicity frequencies, mass-ratio, and physical separation distributions in a consistent parameter space, and compare our results to other PMS populations and the field. Methods. We have obtained adaptive-optics assisted near-infrared observations with NACO (ESO/VLT) and IRCAL (Lick Observatory) for at least one epoch of all 113 SACY members. We have identified multiple systems using co-moving proper-motion analysis and using contamination estimates. We have explored ranges in projected separation and mass-ratio of a [3-1000 au], and q [0.1-1], respectively. Results. We have identified 31 multiple systems (28 binaries and 3 triples). We derive a multiplicity frequency (MF) of MF_(3-1000au)=28.4 +4.7, -3.9% and a triple frequency (TF) of TF_(3-1000au)=2.8 +2.5, -0.8% in the separation range of 3-1000 au. We do not find any evidence for an increase in the MF with primary mass. The estimated mass-ratio of our statistical sample (with power-law index gamma=-0.04 +/- 0.14) is consistent with a flat distribution (gamma = 0). Conclusions. We show further similarities (but also hints of discrepancies) between SACY and the Taurus region: flat mass-ratio distributions and statistically similar MF and TF values. We also compared the SACY sample to the field (in the separation range of 19-100 au), finding that the two distributions are indistinguishable, suggesting a similar formation mechanism.

Sacy — A Search for Associations Containing Young Stars

The scientific goal of the SACY (Search for Associations Containing Young-stars) was to identify possible associations of stars younger than the Pleiades Association among optical counterparts of the ROSAT X-ray bright sources. High-resolution spectra for possible optical counterparts later than G0 belonging to HIPPARCOS and/or TYCHO-2 catalogs were obtained in order to assess both the youth and the spatial motion of each target. More than 1000 ROSAT sources were observed, covering a large area in the Southern Hemisphere. The newly identified young stars present a patchy distribution in UVW and XYZ, revealing the existence of huge nearby young associations. Here we present the associations identified in this survey.