Spectroscopic monitoring of the Herbig Ae star HD 104237

Astronomy and Astrophysics, 2001

We have determined the orbit of the double-lined spectroscopic binary RX J1603.8-3938. The binary consists of two weak-line T Tauri stars, both of which have a spectral type between K3 and K4. The period of the circular orbit is 7.55626 ± 0.00021 days and the mass ratio 0.9266 ± 0.0063. To our knowledge RX J1603.8-3938 is thus the pre-main sequence binary with the longest period that has a circular orbit. Despite the fact that the masses and spectral types of the two components are almost identical, the photospheric lines are much stronger in one component than in the other. In the wavelength region between 5500 and 7800Å we find that the ratio of the equivalent widths of the primary to the secondary is 0.60 ± 0.03. This ratio is constant in time, and is the same for all photospheric lines. Since the components are weak-line T Tauri stars, the effect cannot be explained by any kind of veiling. We are led to the conclusion that the secondary is 0.55± 0.05 mag fainter than the primary. It thus turns out that evolutionary tracks of pre-main sequence single stars are unable to explain the position of this system in the HR diagram.

IEEE Journal of Quantum Electronics, 1999

We present results of the spectroscopic monitoring of AB Aur obtained during the MUSICOS 96 campaign. The analysis is mainly focussed on the He I D3 line, on the Hα line, and on a set of photospheric lines. The star was monitored irregularly for more than 200 hours. We confirm the high level of variability of spectral lines in AB Aur. We find that the photospheric lines have a profile differing significantly from a classical rotational profile. The dominant features of this abnormal photospheric profile are a blue component, in absorption, whose velocity is modulated with a 34hr period, and a red component, stable in velocity but of variable intensity, with a possible periodicity near 43 hrs. The He I D3 line exhibits two well-defined components: a blue component, always in emission with a velocity modulated with a 45hr period, and a red component of variable intensity, alternatively in emission and in absorption, occurring at a fixed velocity, with a variable intensity possibly modulated with a 45 hr period. The Hα line, showing a P Cygni profile, also exhibits pseudo-periodic variations of its blue absorption component, but its variability appears more complicated than that of the other lines studied here. We suggest that the blue component of the photospheric lines is modulated by the star's rotation, with a period of 34 hrs, due to a highly inhomogeneous photosphere, involving significant radial flows. Our model also involves downflows onto the stellar pole to account for the red components of the photospheric lines and of the He I D3 line. We propose two different interpretations of the behavior of the blue component of the He I D3 line. In the first one, this component is formed in a wind originating from the star's equatorial regions. In this interpretation, the rotation period of the equatorial regions of the star is 45 hrs, implying a 25% surface differential rotation, with the pole rotating faster than the equator. The second interpretation involves a wind originating from a region of a circumstellar disk, at a distance of 1.6 stellar radii from the star's center, with a rotation period of 45 hrs. We are not able to decide which one of these two interpretations is more likely, on the basis of the data presented here. Based on observations obtained during the MUSICOS 96 MUlti-SIte COntinuous Spectroscopic campaign, collected at the Canada-France Hawaii, the McDonald 2.1m, the La Palma 2.5m Isaak Newton, the Observatoire de Haute-Provence 1.93m, the Xinglong 2.16m, and the Ritter Observatory 1m telescopes

Astronomy and …, 2004

HD 35929 is a pre-main-sequence Herbig Ae star candidate that exhibits emission in the Hα line and a weak IR excess. Although its luminosity type was estimated as TV from low-resolution spectroscopy, the insignificant HIPPARCOS parallax (0.88 ± 0.93 mas) contradicted the low luminosity. To resolve this discrepancy, we took 3 high-resolution optical spectra of the star (region 5200-6915 Å, R ~ 60 000) and used an archival one (4000-6800 Å, R ~ 48 000). Our analysis of the spectral and photometric information shows that HD 35929 is an F2 III star with T eff = 6880 ± 100 K, log g = 3.3 ± 0.1, log L/L⊙ = 1.7 ± 0.2, v sin i = 70 ± 5 km s −1 , M = 2.3 ± 0.2 M⊙, a mild metal deficit [Fe/H] = −0.2 ± 0. 1, and a weak interstellar reddening (A V ~ 0.1 mag) at a distance D = 345 ± 60 pc. These results confirm an earlier suggestion by Marconi et al. (2000) that HD 35929 is located within the instability strip. At the same time, we argue that it is not a young object, but rather a post-main-sequence giant. The fundamental parameters and IR excess of HD 35929 are similar to those of HD 19993, an emission-line late A-type giant recently discovered by us (Miroshnichenko et al. 2003). These objects might represent a group of evolved intermediate-mass stars with an enhanced mass loss.

The Astronomical Journal, 2004

Extensive photometric and spectroscopic observations have been obtained for HS 1136+6646. The observations reveal a newly formed post-common-envelope binary system containing a hot $DAO.5 primary and a highly irradiated secondary. HS 1136+6646 is the most extreme example yet of a class of short-period hot H-rich white dwarfs with K-M companion systems such as V471 Tau and Feige 24. HS 1136+6646 is a double-line spectroscopic binary showing emission lines of H i, He ii, C ii, Ca ii, and Mg ii, due in part to irradiation of the K7 V secondary by the hot white dwarf. Echelle spectra reveal the hydrogen emission lines to be double-peaked with widths of $200 km s À1 , raising the possibility that emission from an optically thin disk may also contribute. The emission lines are observed to disappear near the inferior conjunction. An orbital period of 0:83607 AE 0:00003 days has been determined through the phasing of radial velocities, emission-line equivalent widths, and photometric measurements spanning a range of 24 months. Radial velocity measurements yield an amplitude of K WD ¼ 69 AE 2 km s À1 for the white dwarf and K K7V ¼ 115 AE 1 km s À1 for the secondary star. In addition to orbital variations, photometric measurements have also revealed a low-amplitude modulation with a period of 113.13 minutes and a semiamplitude of 0.0093 mag. These short-period modulations are possibly associated with the rotation of the white dwarf. From fits of the Balmer line profiles, the white dwarf is estimated to have an effective temperature and gravity of $70,000 K and log g $ 7:75, respectively. However, this optically derived temperature is difficult to reconcile with the far-UV spectrum of the Lyman line region. Far Ultraviolet Spectroscopic Explorer spectra show the presence of O vi absorption lines and a spectral energy distribution whose slope persists nearly to the Lyman limit. The extremely high temperature of the white dwarf, from both optical and UV measurements, indicates that the binary system is one of the earliest post-common-envelope objects known, having an age around 7:7 Â 10 5 yr. Although the spectrum of the secondary star is best represented by a K7 V star, indications are that the star may be overly luminous for its mass.

Astronomy & Astrophysics, 2013

Context. In recent years, HgMn stars have attracted attention after in several of them surface chemical spots of different elements were discovered, whose origin and possible connection with binarity and magnetic fields is not clear yet. Aims. We perform a complete study of the HgMn binary HD 161701, including the determination of physical parameters and photospheric chemical abundances. Methods. We analyzed time series of high-resolution spectroscopic observations obtained with ESO's spectrograph FEROS and the spectro-polarimeter HARPS, in addition to a near-IR spectrum obtained with CRIRES. Radial velocity curves for both stars were combined with additional spectroscopic information to estimate absolute stellar parameters. A spectral separation technique was applied, which enabled us to conduct a detailed spectral analysis of both the HgMn primary and the low-luminosity secondary component, which turned out to be a peculiar star as well. Chemical abundances were determined by spectral synthesis. Using HARPS and FEROS spectra obtained at 11 rotational phases, we detected line profile variations in both stellar companions, indicating a nonuniform surface distribution of chemical composition. Results. HD 161701 is a binary system formed by two chemically peculiar stars in an almost circular orbit with a period of 12.451 d. The primary is a 4.0 M star with a chemical pattern typical of HgMn stars with notable overabundances of P, Mn, Ga, Y, Xe, and Hg. The secondary is a 2.4 M star showing moderate (1−2 dex) overabundance in metals of the iron group, and strong (2−5 dex) overabundaces in Sr, Y, and particularly rare-earth elements. This star presents a remarkable surface chemical spot pattern with Ti and rare-earths concentrated on the surface region that is pemanently facing the binary companion, and Fe concentrated on the far side. The primary star shows weak profile variations in Mn and Cr spectral lines. Conclusions. The coincidence of chemical spots with the position of the binary companion, a fact that has recently been reported also in a few other chemically peculiar stars, suggests a possible connection between the presence of the companion and the origin of chemical anomalies.

Proceedings of the International Astronomical Union, 2004

HD 34282 has been found to pulsate during a systematic search for short-term photometric variability in Herbig Ae/Be stars with the goal of determining the position and size of the pre-Main Sequence instability strip. Simultaneous Strömgren photometry is used in the frequency analysis, yielding two frequencies with values of ν1 = 79.5 and ν2 = 71.3 cycle d −1. The main period, with a value of 18.12 min, represents the shortest period observed up to now for a δ Scuti-type pulsator. A preliminary seismic modelling, including instability predictions and rotation effects, has been attempted. Both, Main Sequence and pre-Main Sequence models predict modes in the range of 56 to 82 cycle d −1 (between 648 and 949 µHz), corresponding to oscillations of radial order n from 6 to 8. The mode identification is not discriminating due to the large error bars attached to the data, therefore, all possible non-radial and radial modes up to = 3 are compatible with the observed oscillations.

We analyze HST/GHRS spectra of AB Doradus, the prototypical ultra-rapidly rotating K dwarf. We observed chromospheric (Mg II) and transition region (C II, Si IV, C IV, and N V) lines periodically throughout the stellar rotation period, and provide a low dispersion stellar atlas of 78 emission lines. The quiescent line profiles of the chromospheric and transition region lines show narrow cores superposed on very broad wings. The broad wings of the Mg II k & h lines and of the transition region lines can be explained by emission from gas co-rotating with the star and extending out to near the Keplerian co-rotation radius (2.8 stellar radii). While this is not a unique solution, it is consistent with previous studies of Hα emission that are naturally explained by large co-rotating prominences. We find no evidence for rotational modulation of the emission line fluxes. The density diagnostics suggest that the transition region is formed at constant pressure, with an electron density 2-3 × 10 12 cm −3 at a temperature of 3×10 4 K. The electron pressure is about 100 times larger than that for the quiet Sun. The emission measure distribution shows a minimum between log(T) = 5 and 5.5. The Mg II 1 GHRS Investigation Definition Team -4line exhibits three interstellar absorption components along the 15 pc line of sight. We identify the lowest velocity component with the G cloud, but the other components are not identified with any interstellar clouds previously detected from other lines of sight.

Monthly Notices of the Royal Astronomical Society, 1999

We present the results of high-resolution spectroscopic, low-resolution spectrophotometric and spectropolarimetric and broad-band multicolour observations of four B-type stars (HD 4881, 5839, 224648 and 179218) and two A-type stars (HD 32509 and 184761) with strong far-infrared (IR) excesses. The excess in HD 184761, which is located at a distance of 65 pc from the Sun, was recognized for the ®rst time. Double-peaked Ha emission line pro®les are found in HD 4881 and HD 5839, while HD 184761, HD 224648 and HD 32509 display no emission in Ha. The remarkable variations observed in the Ha pro®le of HD 179218 are also observed in some classical Be and Herbig Ae/Be stars. An intrinsic component of polarization is clearly present in HD 179218, only an interstellar component is detected in HD 4881 and HD 224648, and HD 184761 was found to be unpolarized. Improved effective temperatures for all six objects were derived. Parallaxes measured by the Hipparcos satellite were used to determine positions of the stars in the HR diagram. HD 4881 and HD 5839 are an order of magnitude more luminous than main-sequence stars of similar temperatures and are most likely newly discovered classical Be stars. Study of the high-resolution IRAS maps and modelling of the spectral energy distributions of HD 4881, HD 5839 and HD 224648 suggest that the observed large IR excesses are caused by radiation from circumstellar dust rather than free±free radiation or infrared cirrus, so they may be higher mass counterparts of b Pictoris stars. HD 32509, HD 224648 and HD 184761, which have very small near-IR excesses, are probably young main-sequence stars. HD 179218, which exhibits the largest near-and far-IR excess in the sample, is an isolated pre-main-sequence Herbig Be star.

The Astrophysical Journal, 2002

We present new spectroscopic observations of the detached late-type double-lined eclipsing binary YY Gem (P = 0.814 days), a member of the Castor sextuple system and one of the benchmarks for the comparison between observations and stellar evolution theory in the lower main-sequence. In addition, we have re-analyzed existing light curves in several passbands using modern techniques that account for the conspicuous presence of spots. This, combined with the spectroscopy, has yielded a very precise determination of the absolute dimensions of the components, which are virtually identical to each other. We obtain for the mean mass, radius, and effective temperature the values M = 0.5992 ± 0.0047 M ⊙ , R = 0.6191 ± 0.0057 R ⊙ , and T eff = 3820 ± 100 K. Both the mass and the radius determinations are good to better than 1%, which in the case of the radius represents a fourfold improvement over previous results and significantly enhances the value of this quantity for testing the models. We discuss the importance of systematic effects in these measurements, by comparison with another high-precision determination of the mass by . A re-analysis of the Hipparcos transit data for Castor AB that accounts for the relative motion of the pair in its 467 yr-period orbit has yielded an improved parallax for the system of 66.90 ± 0.63 mas. With this, we have estimated the age (∼370 Myr) and metal abundance ([Fe/H] ∼ 0.0) of YY Gem from isochrone fits to Castor A and B under the assumption of a common origin. This, along with the other physical properties, allows for an unusually stringent test of the models for low-mass stars. We have compared the observations of YY Gem with a large number of recent theoretical calculations, and we show that all models underestimate the radius by up to 20%, and most overestimate the effective temperature by 150 K or more. Both of these trends are confirmed by observations of another similar system in the Hyades cluster (V818 Tau). Consequently, theoretical ages for relatively low-mass objects such as T Tauri stars derived by placing them on the H-R diagram may be considerably biased. If the radius is used directly as a measure of evolution, ages could be underestimated by as much as a factor of 10 in this mass regime. In view of these discrepancies, absolute ages from essentially all current models for the lower main sequence must be viewed with at least some measure of skepticism. Finally, we derive a new and very accurate ephemeris based on all available times of eclipse, and we lay to rest previous claims of sudden changes in the orbital period of the binary, which we show to be spurious.

Astrophysics and Space Science, 2016

While monitoring a sample of apparently slowly rotating superficially normal bright late B and early A stars in the northern hemisphere, we have discovered that HD 67044 and HD 42035, hitherto classified as normal late B-type stars, are actually respectively a new chemically peculiar star and a new spectroscopic binary containing a very slow rotator HD 42035 S with ultra-sharp lines (v e sin i = 3.7 km s −1) and a fast rotator HD 42035 B with broad lines. The lines of Ti II, Cr II, Mn II, Sr II , Y II, Zr II and Ba II are conspicuous features in the high resolution SOPHIE spectrum (R = 75000) of HD 67044. The Hg II line at 3983.93Å is also present as a weak feature. The composite spectrum of HD 42035 is characterised by very sharp lines formed in HD 42035 S superimposed onto the shallow and broad lines of HD 42035 B. These very sharp lines are mostly due to light elements from C to Ni, the only heavy species definitely present are strontium and barium. Selected lines of 21 chemical elements from He up to Hg have been synthesized using model atmospheres computed with ATLAS9 and the spectrum synthesis code SYNSPEC48 including hyperfine structure of various isotopes when relevant. These synthetic spectra have been adjusted to high resolution high signal-tonoise spectra of HD 67044 and HD 42035 S in order to derive abundances of these key elements. HD 67044 is found to have distinct enhancements of Ti,