With the advent of high-resolution infrared spectrographs, radial relocity (RV) searches enter into a new domain. As of today, the most important technical question to address is which wavelength reference is the most suitable for high-precision RV measurements. In this work we use atmospheric absorption features as wavelength reference on CRIRES data obtained on two programs and three different targets. We analyzed the data from the TW Hya campaign again, reaching a dispersion of about 6 m/s on the RV standard on a time scale of roughly 1 week. We confirm that there is a low-amplitude RV signal on TW Hya itself, with an amplitude roughly 3 times smaller than the one reported at visible wavelengths. We present RV measurements of Gl 86 as well, showing that our approach is capable of detecting the signal induced by a planet and correctly quantifying it. Our data show that CRIRES is capable of reaching an RV precision of less than 10 m/s on a time scale of one week. The limitations of this particular approach are discussed, along with the limiting factors on RV precision in the IR in a general way. The implications of this work on the design of future dedicated IR spectrographs are addressed as well.

Abstract. In this paper we present an updated compilation of the currently known pre-main sequence (PMS) spectroscopic binaries (SB) for which orbital elements have been determined. In particular we report our results for and discuss the case of the bona-fide PMS system RX J1603.9-3938, which has a circular orbit and a period of 7.56 days. This is the longest orbital period for a circular orbit found among the bona-fide PMS spectroscopic binaries so far, and we suggest that this system may be thus considered to now set the PMS circularization period. The longer period is compatible with the circularization periods already known for older binary populations such as the Hyades and Praesepe. When considered in the context of the circularization periods for other binary populations of different ages, the new PMS circularization period strongly supports the suggestion of Mathieu et al. (1992) that a hybrid scenario (tidal circularization occurring on both PMS phase and on MS phase) could explain the observed circularization periods as a function of age. The apparently circular orbit observed in another PMS system, RX J1301.0-7654a, with an orbital period of nearly 13 days, may perhaps change this picture when the orbit is improved and the system is better understood.

No abstract

Ultra-short-period (USP) exoplanets have orbital periods shorter than one day. Precise masses and radii of USPs could provide constraints on their unknown formation and evolution processes. We report the detection and characterization of the USP planet GJ 367b using high precision photometry and radial velocity observations. GJ 367b orbits a bright (V-band magnitude = 10.2), nearby, red (M-type) dwarf star every 7.7 hours. GJ 367b has a radius of 0.718 ± 0.054 Earth-radii, a mass of 0.546 ± 0.078 Earth-masses, making it a sub-Earth. The corresponding bulk density is 8.106 ± 2.165 g cm -3 , close to that of iron. An interior structure model predicts the planet has an iron core radius fraction of 86 ± 5%, similar to Mercury's interior. Main Text:Red dwarf stars of spectral type M (M dwarfs) are cool stars with effective temperatures (Teff) below ~4000 K (1). They have masses and radii less than around ~60% of the Sun's and are the most abundant type of stars in the solar neighborhood (2-4). It has been estimated that M dwarfs host an average of 2.5 ± 0.2 small planets [planet radius Rp < 4 Earth-radius (R⊕)] with periods less than 100 days (5). Due to the small stellar radius, the transit signal produced

Abstract. In recent years. we have spectroscopically observed thousands of counterparts of selected ROSAT bright sources in the sacy project (Search for Associations Containing Young stars). We demonstrated that hundreds of the young stars found this way belong to nearby young, loose associations, some detected only in sacy, with ages in the range from 5 to 100 Myr. For their ages, these associations show no trace of their primitive nurseries, which poses some difficulties as to their origins. Nevertheless, there are some associations clearly associated with young open clusters, such as the ε Cha association (6 Myr) with the η Cha cluster, and the Argus association with IC 2391 (40 Myr). There seem to exist also more subtle connections, such as the AB Dor association (75 Myr) with the Pleiades. Here, we present evidence of the connections of young associations to open clusters, to understand their origin and their possible insertion in the cluster infant-mortality and Gould Belt scenarios.

Abstract. We report the discovery of the first low-mass pre-main sequence eclipsing binary among a sample of double-lined spectroscopic binaries in the Orion star forming region found in a previous high-resolution spectroscopic investigation on ROSAT-discovered weak-T Tauri stars. Here we present the preliminary results from the combined analysis of the spectroscopic orbit and B and V light-curves, using data available till spring 2000. We then compare the fundamental stellar parameters derived from the orbital solution with those inferred from some widely used theoretical evolutionary models.

Abstract. We present nearly 70 new observations for M67 members at the main-sequence (MS), turn-off (TO) and post-turn-off (PTa) in addition to those already published in Melo, Pasquini & De Medeiros (2001). These additional v sin i measurements confirm that most of stars are experiencing a strong braking as they pass the turn-off. In contrast to our previous results, some spread in the v sin i is observed among the TO and PTa stars.

We present new observations of projected rotational velocities of main sequence B stars in the galactic clusters NGC 2439, NGC 3293, NGC 3766, NGC 4755, NGC 7160 and h & χ Persei. 257 stars have been observed with three instruments, 207 of which are presented here. Projected rotational velocities have been determined by least-squares fit to synthetic spectra. Our v sin i scale is compared with that of Slettebak et al. (1975).