Spectre continu dans le proche infrarouge de deux étoiles Be: HD 50138 et HD 51585

Continuous spectra of the Be objects HD 50138 and HD 51585 have been investigated between 1.6 and 1.2 ^-1. The infrared gradient _IR of HD 50138 (B5eV) is found to be 2.09±0.10, while the typical B5V star And indicates _IR=1.17. A B5V (HD 16219) star located at about the same distance as HD 50138 has _IR=1.29 and it is shown that interstellar reddening may account for _IR between HD 16219 and And. The difference in gradient between HD 50138 and HD 16219 ( _IR=0.8) may be explained by a continuous reemission in a lenticular envelope with a radius equal to 4R _*. The peculiar object HD 51585 exhibits a B0.5 continuous spectrum, for which the value d logI /d(1/) should be 1.13 according to model atmospheres computations. The distance as derived from color excess leads to disagreement between measured and computed (for a B0.5 star) values of d logI /d(1/). The reddening may be explained by reemission in an envelope the radius of which is smaller than 5R_*. In conclusion, the narrowness of the spectral range under consideration does not permit to decide whether the observed reddening is due to recombination to the third level of the hydrogen atom or whether it is part a thermal reemission in a circumstellar cloud at lower temperature, as it has been observed around 10 by various authors.

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Les spectres utilisés dans ce travail ont été obtenus à l'aide des téléscopes de 193 cm et 120 cm de l'Observatoire de Haute-Provence (CNRS).     

An iras atlas of ysos in nearby dark clouds

We are using the newIRAS Sky Survey Atlas to construct a catalog of Galactic dark clouds and their associated Young Stellar Objects (YSOs). FromIRAS 100 and 60µm data we calculate images of the 100µm optical depth distribution in the clouds. Using theIRAS Faint Source Catalog we identify sources which have colors indicative of YSOs and have positions that lie inside cloud boundaries in the optical depth images. Here we present some preliminary results of applying this analysis to the Chamaeleon dark cloud complex.     

Study of the IR-excess supergiant HD 331319

We report the discovery of brightness variability in the IR-excess early F supergiant HD 331319, a candidate post-AGB star. Over three years of systematic U BV observations, the star showed low-amplitude (up to in V) quasi-periodic brightness variations on a time scale of ∼45 days. A preliminary analysis of our photometry indicates that HD 331319 and other typical post-AGBF supergiants have a similar pattern of variability. A study of the extinction toward HD 331319 leads us to conclude that the fraction of the circumstellar extinction is small for this star. We present low-resolution spectroscopy for HD 331319 and discuss the spectral classification of post-AGB F supergiants using HD 331319, HD 161796, HD 187885, and HD 56126 as examples.     

Soft X-ray observation of theϱ ophiuchus dark cloud region

Soft X-rays (0.1–0.8 keV) from the region including the Oph dark cloud were observed with the SAS-3 low-energy X-ray telescope. No X-ray absorption by the cloud was observed. This indicates that the diffuse component of soft X-rays in this region is mostly from the foreground of the Oph cloud which is located at a distance of 160–200 pc.     

The spectrum of the Bp star HD 36916

The spectrum of the peculiar Bp star HD 36916 has been studied on plates with dispersion 9.7 A/mm and compared with those of Aur, B3V andi And, B8V. A comparison of the observed contours of H, H and of the Balmer discontinuity D with those computed by Mihalas gives the following results: HD 36916: _e=0.347, logg=3.8;i And: _e=0.383, logg=3.2; Aur: _e=0.302, logg=3.6. HD 36916 presents the characteristics of the Si-4200 stars: strong deficiency in helium and probably also in oxygen and nitrogen, strong excess of silicon and strontium; 3984 Hgii is present. Moreover this star also has characteristics which are not common to Si-4200 stars but rather to Mn stars: excess by a factor of ten of the elements of the iron group and an excess larger, probably of the order of 100, for manganese. The star is a member of the Sword subgroup of the Orion association.     

Magnetic Model of HD 2453

A model is constructed for the magnetic field of the star HD 2453, which has a very long rotation period (P=521^d). It is found that the structure of the field corresponds to the model of a dipole shifted by r=0.09R from the center. The angle of inclination of the axis of the dipole to the axis of rotation, =5°; that is, the star is viewed almost from its equator of rotation and magnetic equator. This explains the low amplitude of the phase dependence of the magnetic field, Be(P), and the low amplitude of the photometric variability. The field at the magnetic poles is equal to Bp=+4400 and -7660 G. The magnetic field parameters turn out to be close to those obtained by Landstreet and Mathys assuming a dipole-quadrupole-octupole model. A Mercator map of the magnetic field distribution of HD 2453 is produced.     

Observations spectroscopiques de HD 50138

Observations of the Be star HD 50138 have been extended to the photographic infrared region up to 9500 Å. The main features noted in this wavelength range are strong lines of Oi (8446 Å), Hi (from P 9 to P 20), the Caii infrared triplet and the 8629 line attributed to Ni. The 7772 multiplet of Oi is shown to undergo important changes during the period of observations (1959–1971). Higher Balmer lines do not exhibit any emission component, but their profiles are variable and indicate the presence of satellite absorption, as already mentioned by some authors.Les observations ont été obtenues aux télescopes de 120 et 193 cm de l'observatoire de Haute-Provence (CNRS).     

Quantitative analysis and spectral variation of the Ap star HD 151 199

The radial velocity, intensity variations of the Caii line and chemical composition of the suspected magnetic star HD 151 199 have been studied using three 9.6 A/mm and twenty-one 40 A/mm dispersion spectrograms which were taken at St. Michel and Asiago Observatories respectively. The radial velocity and the intensity of the Caii K line suggest a variation with a 6.143 day period. The range is about 40 km/sec for the radial velocity and the K line changes in intensity by 50%. Preliminary results of the photometric data in the Geneva system show a similar trend of variation in (B ₂–B ₁) with the same period. H and H contours and the Balmer discontinuity give _eff=0.50 and logg=4. The most probable microturbulence is found to be 6.4 km/sec. The excitation temperature, _exc=0.50, is derived from the Fe lines and adopted for the other elements as well. A quantitative analysis by curve of growth and weighting function method, using Mihalas and Conti's atmospherical models was made. HD 151 199 shows an overabundance of Ca, Sr, Ba, by factors of 2, 40, and 5 with respect to 30 L Mi. Euii is probably overabundant also but it is not possible to give this element a numerical value. The other elements seem to be normal.     

Physical characters of HD 93044

The measurements ofuvby H of HD 93044 were obtained in April 1991, and the observational results that the star locates nearly in the middle of Scuti instability strip with somewhat deviation to red edge. According to Crawford (1979) and Philip's (1979) calibrations, the effective temperature, absolute visual magnitude and surface gravity are obtained to beT _eff = 7300±200 K,M _v = 1.^m33±0.39 and logg = 3.7±0.15, respectively. The observational results of _m1 = 0.01 give an estimate of [Fe/H] = –0.003 ± 0.18, so the opinion of metallic deficient is not supported obviously. The observations show the reddening indexE(b -y) to be 0.014 which is 1.4 times as large as the standard deviation of Crawford's (1979) statistics.Project supported by Young Foundation of Beijing Astronomical Observatory, China     

Long-Term Spectral Variability of the Herbig Ae-Star HD 179218

The results of high-resolution long-term spectral monitoring of Herbig Ae star HD 179218 in the region of emission H line and the sodium resonance doublet Na I D are presented. The received data show the existence of short-term variability (about 10 days) and long-term wave-like variability of equivalent width EW, intensity of circumstellar (CS) emission I and parameters of H emission profile. The analysis of these data allows us to suppose the existence of the global variability of parameters of accretion disk.     

On interstellar reddening law in the Taurus dark clouds

The interstellar reddening law in the Taurus dark clouds is investigated from visual, infrared, and ground based ultraviolet photometric observations of heavily reddened stars HD 29647, HDE 283701, and HDE 283812. The star HD 29647 located in the center of a very dense dark cloud Khavtassi 278 shows a reddening law which is anomalous in the wavelengths shorter than 400 nm. When combined with observations by Snow and Seab from the IUE it can be represented by a single straight line from 1 m to 250 nm. Other two stars situated in less dense parts of the Taurus dark clouds show normal reddening law.     

The high-galactic-latitude O-type star HD 93521

The spectrum of the peculiar O9 star HD 93521 is studied and compared with those of the standard stars 10 Lac and AE Aur. Several possibilities are examined which might explain the high galactic latitude of this star, corresponding toz>750 pc and its slight helium excess. It is suggested that HD 93521 is a runaway binary system composed of the O9 star plus a neutron star left over from a supernova explosion.     

Magnetic field of CP stars in the Ori OB1 association. II. HD36540, HD36668, HD36916, HD37058

We present the results of magnetic field measurements of four chemically peculiar (CP) stars with helium abundance anomalies which are the members of the Orion stellar association OB1. The stars under study were classified as magnetic by other authors earlier. The present paper contains the results of the extensive study of the stars. Magnetic field measurements allowed us to conclude that HD36540 has a weak field and the longitudinal component B _e does not exceed 500 G. The longitudinal field of HD36668 varies with the period P = 2_. ^d 11884 and the amplitude from ?2 to +2 kG. The magnetic field of HD36916 has mainly negative polarity and varies within the range from 0 to ?1 kG with the period P = 1.d 565238. HD37058 is a magnetic star, the longitudinal field of which varies from ?1.2 to +0.8 kG with the period P = 14_. ^d 659. The B _e field variability pattern for the stars HD36916 and HD37058 is of a simple harmonic type. The longitudinal field of HD36668 is best described with two combined harmonic functions (“a doublewave”). The variability period of HD36540 is still undetermined. For all the stars from this paper, we measured radial velocities V _r, axial rotation rates v _e sin i, and determined basic parameters of atmospheres (effective temperatures T _eff and gravity acceleration log g). We also estimated masses M, luminosities L, and radii R of the stars.     

V792 Her=HD 155638: A totally eclipsing RS CVn binary

Photometry of HD 155638=V792 Her has been analyzed to determine the elements of this totally eclipsing RS CVn binary. The light variation outside eclipse was found to have a period of 27^d.07±0^d.07, which is slightly different from the 27^d.5384±0^d.0045 orbital period. Analysis of the eclipses was achieved by a modification of the Russell-Merrill technique. With the aid of radial velocity measures, absolute elements were obtained for the hot and cool stars, respectively;R _h=2.58R ,R _c=12.28R ,M _h=1.40M ,M _c=1.46M ,i=80^o.61 and velocity semi-amplitudesK _c=48.36 km s^–1±0.79 km s^–1, andK _h=50.50 km s^–1±0.33 km s^–1. The apparent magnitudes areV _h=9 ^m .73 andV _c=8 ^m .48. The distance to HD 155638 was estimated to be 310 parsecs.     

Low‐mass visual binaries in the solar neighbourhood: The case of HD 141272

We search for stellar and substellar companions of young nearby stars to investigate stellar multiplicity and formation of stellar and substellar companions. We detect common proper‐motion companions of stars via multi‐epoch imaging. Their companionship is finally confirmed with photometry and spectroscopy. Here we report the discovery of a new co‐moving (13 σ) stellar companion ∼17.8 arcsec (350AU in projected separation) north of the nearby star HD141272 (21 pc).With EMMI/NTT optical spectroscopy we determined the spectral type of the companion to be M3±0.5V. The derived spectral type as well as the near infrared photometry of the companion are both fully consistent with a M_⊙ dwarf located at the distance of HD141272 (21 pc). Furthermore the photometry data rules out the pre‐main sequence status, since the system is consistent with the ZAMS of the Pleiades. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Rho Ophiuchi cloud — An overview

The relative short distance (165 pc) and considerable mass (2000M ) of the Rho Ophiuchi cloud enable the study of the physical conditions within the cloud with a fine detail as it is reached in few complexes only. On the basis of the observations between 10^–14 and 10^–1 m wavelength, the most remarkable features of the cloud detected are: (1) The cloud represents one of the strongest detectable -ray sources for energies greater than 100 MeV. (2) X-ray observations gave no evidence that the cloud is interacting with a supernovae remnant or a neutron star what was supposed to account for the observed -ray flux. (3) Ultraviolet observations indicate that a considerable number of small particles is present toward the embedded star HD 147889 being placed at the edge of the cloud. (4) The ratio of total to selective extinction isR>4 toward the denser regions of the cloud. (5) An embedded stellar cluster of about 50 stars was detected by four IR-surveys toward the central region of the cloud. (6) Far-IR observations indicate that there are only 3 B-stars within the cloud. The dust-temperature reaches locally 50 K. (7) More than 10 different molecular species were detected by ratio observations. A considerable depletion of heavy elements is observed. There are two dense regions within the cloud which are likely contracting.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986.     

An asymptotic solution for the stellar case of the non-planar three-body problem

A simplified model of the Non-Planer Three-Body Problem is considered in which to particles, forming a close binary, orbit a distant point. A small parameter , related to the distance separating the binary and the remaining mass, is defined. The time is eliminated from the equations of motion and an angular variable is used instead. A three-variable expansion procedure is used to find an asymptotic solution of the problem. It is possible to obtain a solution up to the order six in without secular terms only if the mutual inclinationi ₀ of the unperturbed orbits is less than a critical inclinationi ₁ (i ₁39°).

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Resumé On considère un modèle simplifié du Problème Non-Plan des Trois Corps, dans lequel deux particules, formant une binaire proche, sont en orbite par rapport à un troisième point éloigné des deux autres. On définit un petit paramètre , lié à la distance séparant la binaire de la particule restante. On élimine le temps des équations du mouvement et on utilise une variable angulaire comme nouvelle variable indépendante. Une méthode de développement à trois échelles est utilisée permettant d'obtenir une solution asymptotique du problème. On montre qu'il est possible d'obtenir une solution jusqu'à l'ordre six en sans termes séculaires uniquement si l'inclinaison mutuellei ₀ des orbites non perturbés est inférieure à un angle d'inclinaison critiquei ₁ (i ₁39°).

     

Interstellar extinction in the vicinity of the reflection nebula NGC 1333 in Perseus

The dependence of interstellar extinction on distance in the direction of a dark cloud around the reflection nebula NGC 1333 is determined on the basis of photoelectric Vilnius photometry and photometric classification of 78 stars. Two dust clouds are noted at distances 160 and 220 pc. The first one with mean extinction of 0.4 mag is concluded to belong to the Taurus cloud complex and the second cloud with mean extinction of 1.8 mag belongs to the chain of dark clouds and other young objects which is almost perpendicular to the spiral arm but lies 80 pc below the galactic plane. The star BD +30°549 which illuminates the NGC 1333 nebula is at distance 212 pc from the Sun. No extinction increase behind the Perseus cloud is detected.     

The short time-scale light variability of HD 153919 revisited

Using Fourier analysis techniques, we have analysed all the available sets of visual photometric data concerning the X-ray binary HD 153919. This was made in order to clear up the controversy on the possible existence or absence of the small amplitude light variability (T90 min).In this work, great effort has been made to keep a good level of homogeneity and objectivity. The main conclusion is that at the 99.4% confidence level, a periodicity (=15.5 day^–1) is detected in one data set. In this case, we can safely conclude that the short time-scale variability does exist! No other self-conclusive detection can be definitely reported; nevertheless, at the 90% confidence level, the star has a tendency to vary with characteristic frequencies of 15 day^–1, 30 day^–1 and possibly higher multiples.HD 153919 4U1700-37 V884 Sco.     

The angular momentum problem and magnetic braking during star formation: Exact solutions for an aligned and a perpendicular rotator

The problems of fragmentation, angular momentum, and magnetic flux during star formation are reviewed briefly. Then the resolution of the angular momentum problem through magnetic braking is studied rigorously.A disk-like interstellar cloud of uniform density _cl is given an initial angular velocity _o about its axis of symmetry, which isaligned with an initially uniform, frozen-in magnetic field. Torsional Alfvén waves transport angular momentum from the cloud to the external medium, which has a uniform density _ext . The angular velocity of the cloud ( _cl ) is determined analytically as a function of space and time for different ratios _cl / _ext (the only free parameter in the equations), representing different stages of contraction. Despite dissimilar transient response of the cloud (or fragment) structure to different initial conditions, the characteristic time for magnetic braking of the rotation of the cloud (or fragment) as a whole is remarkably insensitive to the initial conditions and independent of the stage of contraction. The latter conclusion is in agreement with an approximate result obtained recently (Mouschovias, 1978; 1979a).A cylindrical cloud (or fragment) of uniform density is also imparted an initial angular velocity about its axis of symmetry with respect to the external medium. The frozen-in magnetic field is now initially radial andperpendicular to the axis of symmetry. In this case magnetic braking becomes more efficient upon contraction. It is more efficient than the aligned rotator case typically by one order of magnitude. The angular momentum problem can be resolved in about 10⁶ yr during the early stages of cloud contraction. Planetary systems, such as the Sun-Jupiter pair, become dynamically possible. A stage exists in which a cloud (or fragment) is in retrograde rotation with respect to its surroundings. This provides the first and only observable prediction of magnetic braking in action. It also constitutes a natural explantation of retrograde rotation in stellar and planetary systems.This work was supported in part by the National Science Foundation under grant NSF AST-77-23568.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy.