scholarly journals Open clusters

2018 ◽  
Vol 610 ◽  
pp. A30 ◽  
Author(s):  
Y. Aidelman ◽  
L. S. Cidale ◽  
J. Zorec ◽  
J. A. Panei
Keyword(s):  
Spectral Type ◽  
Circumstellar Disks ◽  
Spectrophotometric Study ◽  
Open Clusters ◽  
Distance Modulus ◽  
Be Stars ◽  
Circumstellar Envelopes ◽  
B Stars ◽  
Fundamental Parameters ◽  
Color Excess

Context. Stellar physical properties of star clusters are poorly known and the cluster parameters are often very uncertain. Aims. Our goals are to perform a spectrophotometric study of the B star population in open clusters to derive accurate stellar parameters, search for the presence of circumstellar envelopes, and discuss the characteristics of these stars. Methods. The BCD spectrophotometric system is a powerful method to obtain stellar fundamental parameters from direct measurements of the Balmer discontinuity. To this end, we wrote the interactive code MIDE3700. The BCD parameters can also be used to infer the main properties of open clusters: distance modulus, color excess, and age. Furthermore, we inspected the Balmer discontinuity to provide evidence for the presence of circumstellar disks and identify Be star candidates. We used an additional set of high-resolution spectra in the Hα region to confirm the Be nature of these stars. Results. We provide Teff, log g, Mv, Mbol, and spectral types for a sample of 68 stars in the field of the open clusters NGC 6087, NGC 6250, NGC 6383, and NGC 6530, as well as the cluster distances, ages, and reddening. Then, based on a sample of 230 B stars in the direction of the 11 open clusters studied along this series of three papers, we report 6 new Be stars, 4 blue straggler candidates, and 15 B-type stars (called Bdd) with a double Balmer discontinuity, which indicates the presence of circumstellar envelopes. We discuss the distribution of the fraction of B, Be, and Bdd star cluster members per spectral subtype. The majority of the Be stars are dwarfs and present a maximum at the spectral type B2-B4 in young and intermediate-age open clusters (<40 Myr). Another maximum of Be stars is observed at the spectral type B6-B8 in open clusters older than 40 Myr, where the population of Bdd stars also becomes relevant. The Bdd stars seem to be in a passive emission phase. Conclusions. Our results support previous statements that the Be phenomenon is present along the whole main sequence band and occurs in very different evolutionary states. We find clear evidence of an increase of stars with circumstellar envelopes with cluster age. The Be phenomenon reaches its maximum in clusters of intermediate age (10–40 Myr) and the number of B stars with circumstellar envelopes (Be plus Bdd stars) is also high for the older clusters (40–100 Myr).

scholarly journals B stars in open clusters: fundamental parameters

2010 ◽  
Vol 6 (S272) ◽  
pp. 276-277
Author(s):  
Yael Aidelman ◽  
Lydia S. Cidale ◽  
Juan Zorec ◽  
María L. Arias
Keyword(s):  
Classification System ◽  
Open Cluster ◽  
Open Clusters ◽  
Distance Modulus ◽  
Spectral Classification ◽  
B Stars ◽  
Fundamental Parameters ◽  
Complete Study

AbstractWe use the BCD spectrophotometric classification system to derive fundamental parameters of B stars in NGC 2439, NGC 3766 and NGC 6087. We are able to perform a complete study of each open cluster by deriving spectral classification of its members, distance modulus and age as well.

scholarly journals Be Stars as Members of Open Clusters

1987 ◽  
Vol 92 ◽  
pp. 500-502
Author(s):  
A. Feinstein
Keyword(s):  
Main Sequence ◽  
Absolute Magnitude ◽  
Open Clusters ◽  
Distance Modulus ◽  
Be Stars ◽  
Spectral Classification ◽  
Magnitude Diagram ◽  
Color Excess ◽  
Be Star ◽  
The Mean

A list of 124 Be-type stars belonging to 52 open clusters has been compiled. All of them have photometric UBV data, and many of them spectral classification in the MK system. Besides, the cluster's distance modulus and the mean color excess from the member stars are known. Then, we have computed the absolute magnitude and the intrinsic colors of each Be star.The observed color-color diagram (Figure 1) shows clearly that nearly all Be stars appear to be reddened. In Figure 2 is given the color-magnitude diagram, (B-V)o versus Mv, in whicn the ZAMS (Blaauw, 1963) is also included. A few stars to the left of the main sequence belong to the young open clusters: NGC 869, 6167, 6530 and 6611. This effect may be due to wrong correction of the color indices because of abnormal values of the reddening law.

scholarly journals Hipparcos Positions of B/Be Stars on the HR Diagram

2000 ◽  
Vol 175 ◽  
pp. 117-128 ◽  
Author(s):  
Danielle Briot ◽  
Noel Robichon
Keyword(s):  
Spectral Type ◽  
Rotational Velocity ◽  
Absolute Magnitude ◽  
Be Stars ◽  
Class V ◽  
B Stars ◽  
Luminosity Class ◽  
The Mean ◽  
Absolute Magnitudes ◽  
Hipparcos Parallax

AbstractAbsolute magnitudes of Be and B stars are computed for each spectral type and luminosity class V and IV, using the Hipparcos parallax measurements. Some simulations have been carried out in order to estimate the effects which could bias the mean absolute magnitude calculations. As a result, only stars with σπ/π < 15% have been used. A first result is that B stars are fainter than previous estimations by about 0.5 magnitude on average. We then observe that on average Be stars are brighter than B stars of the same spectral type and this over-luminosity increases with the spectral type. A possible interpretation is proposed based on the fact that the rotational velocity of the late Be stars is near the critical rotational velocity.

scholarly journals Main-sequence broadening, Be stars, and stellar rotation inhand χ Persei

1994 ◽  
Vol 162 ◽  
pp. 151-152
Author(s):  
J. Denoyelle ◽  
C. Aerts ◽  
C. Waelkens
Keyword(s):  
Main Sequence ◽  
Large Fraction ◽  
Variable Stars ◽  
Theoretical Studies ◽  
Be Stars ◽  
Stellar Rotation ◽  
B Stars ◽  
Fundamental Parameters ◽  
Magnitude Diagram ◽  
Double Cluster

The double cluster h andxPersei is one of the richest clusters containing early-B stars, and therefore is important for observational and theoretical studies on the fundamental parameters of massive stars. The colour-magnitude diagram of the double cluster shows an important scatter (see Figure 1). It has long been known thathandxPersei are extremely rich in Be stars (Slettebak 1968). Our previous contention (Waelkens et al. 1990) that the large-amplitude variable stars we discovered are also Be stars, could be confirmed for a few objects. Rotation velocities for stars inhandxPersei are usually high, which is not surprising in view of the large fraction of Be stars.

scholarly journals The number of Be stars compared with the number of B stars, taking into account the specific physical characteristics of Be stars

1994 ◽  
Vol 162 ◽  
pp. 356-357
Author(s):  
D. Briot ◽  
J. Zorec
Keyword(s):  
Spectral Type ◽  
Bright Star ◽  
Physical Parameters ◽  
Emission Characteristics ◽  
Be Stars ◽  
Constant Mass ◽  
B Stars ◽  
The Past ◽  
Star Catalogue

It is very important for the understanding of the Be phenomenon, and particularly for locating a possible Be phase in the evolutionary track of B stars, to accurately determine the proportion of Be stars among all B stars. This type of study was already made several times in the past. Results obtained generally show a maximum Be frequency around spectral type B2 then a decrease towards late spectral types. Actually Be stars do not have the same characteristics as “normal” B stars and we have to take this into account in the determination of the ratio : number of Be stars / number of B stars. We use the Bright Star Catalogue (Hoffleit & Jaschek 1982) and the Supplement to the Bright Star Catalogue (Hoffleit, Saladyga & Wlasuk 1983) containing stars V= 7.10 and brighter. This study needed to be made separately for the different spectral types because:- Physical parameters of B stars are very different from B0 to B9;- Emission characteristics of Be stars vary very much, with a decrease from B0e to B9e.We successively consider three effects which can influence the frequency of Be stars:- The over-luminosity of Be stars as compared with B stars;- Spectral type changes during constant mass evolution;- Spectral type changes due to the fast rotation of Be stars.

scholarly journals The Visual Absolute Magnitude of the Central Objects in Be Stars

2000 ◽  
Vol 175 ◽  
pp. 55-58 ◽  
Author(s):  
A. Moujtahid ◽  
J. Zorec
Keyword(s):  
Absolute Magnitude ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Circumstellar Envelopes ◽  
Energy Distributions ◽  
B Stars ◽  
Absolute Magnitudes ◽  
Magnitude Difference ◽  
Good Agreement ◽  
The Continuum

AbstractUsing the circumstellar envelope parameters (mean temperature, extent and opacity) derived by fitting theoretical energy distributions to those observed in a sample of 20 Be stars, we estimate the respective magnitude difference ΔV = V – V* of the continuum flux excess produced by their circumstellar envelopes. Using then the HIPPARCOS parallaxes of these stars and the ISM E(B-V) colour excesses derived with the surrounding normal B stars, we estimate the visual absolute magnitude of the central objects in the program Be stars. In most cases the results obtained are in good agreement with the absolute magnitudes obtained from the photospheric (λ1, D) components derived in the BCD spectrophotometric system. There are, however, strong discrepancies in 4 program stars which deserve further studies. The magnitude excess seems to be ΔV ≲ 0 for the higher effective temperatures only. There is no correlation between ΔV and Vsin i, as would be expected if the circumstellar envelopes were strongly flattened.

scholarly journals Variation of Anomalous Stages of Ionization with Spectral Type for Be Stars

1982 ◽  
Vol 98 ◽  
pp. 387-390 ◽  
Author(s):  
J. M. Marlborough ◽  
Geraldine J. Peters
Keyword(s):  
Spectral Type ◽  
Uv Spectra ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Uv Astronomy ◽  
B Stars ◽  
Stellar Radiation ◽  
Wide Range

One of the interesting results of ultraviolet (UV) astronomy was the discovery of ions from unexpected stages of ionization in spectra of O,B stars. The most common ions concerned are O VI and N V, but also C IV and Si IV in B stars. The presence of these ions is anomalous because generally their abundance is expected to be negligible if they are produced by photoionization by stellar radiation, either in the photosphere or in a cool circumstellar envelope (CE). The same ions are observed in the UV spectra of Be stars. Previous investigations, largely with Copernicus spectra, have reported O VI and N V in late Oe and early Be stars and Si IV in stars as cool as B5 (Marlborough, 1981 and references therein). In this paper we present the results of a preliminary survey of IUE spectra of Be stars covering a wide range of spectral type.

scholarly journals Continuous spectra of circumstellar envelopes of Be stars

1994 ◽  
Vol 162 ◽  
pp. 425-426
Author(s):  
D. Rohe-Koths ◽  
J. Dachs
Keyword(s):  
Line Emission ◽  
Circumstellar Disks ◽  
Balmer Line ◽  
Be Stars ◽  
Continuous Emission ◽  
Circumstellar Envelopes ◽  
Recombination Radiation ◽  
Infrared Spectral ◽  
Be Star ◽  
Central Stars

Line emission in Be star spectra is accompanied by continuous emission both in the Balmer continuum and in the infrared spectral region, due to the same process that is responsible for Balmer line emission, i.e. to recombination radiation from ionized hydrogen in the extended circumstellar disks surrounding the hot central stars.

scholarly journals Interferometric survey of Be stars with the CHARA array

2010 ◽  
Vol 6 (S272) ◽  
pp. 634-635 ◽  
Author(s):  
Yamina N. Touhami ◽  
Douglas R. Gies ◽  
Gail H. Schaefer ◽  
Noel D. Richardson ◽  
Stephen J. Williams ◽  
...  
Keyword(s):  
Rotational Velocity ◽  
Circumstellar Disks ◽  
Geometrical Parameters ◽  
Be Stars ◽  
Circumstellar Envelopes ◽  
Disk Model ◽  
Spatially Resolved ◽  
Near Ir ◽  
Be Star ◽  
Chara Array

AbstractWe present the first spatially resolved observations of circumstellar envelopes of 25 bright northern Be stars. The survey was performed with the CHARA Array interferometer in the K-band at intermediate and long baselines. The interferometric visibilities are well fitted by a viscous disk model where the gas density steeply decreases with the radius. Physical and geometrical parameters such as the density profile, the inclination, and the position angles of the circumstellar disks are determined. We find that the density radial exponent ranges between n ≈ 2.4 − 3.2, which is consistent with previous IRAS measurements. We have also obtained simultaneous optical and near-IR spectrophotometric measurements, and found that the model reproduces well the observed disk IR-continuum excess emission. By combining the projected rotational velocity of the Be star with the disk inclination derived from interferometry, we give estimates of the equatorial rotational velocities of these Be stars.

scholarly journals Pseudo-photometric distances of 30 open clusters

2018 ◽  
Vol 619 ◽  
pp. A132 ◽  
Author(s):  
A. Chelli ◽  
G. Duvert
Keyword(s):  
Spectral Type ◽  
Large Scale ◽  
Open Cluster ◽  
Estimation Method ◽  
Distance Estimation ◽  
Open Clusters ◽  
Distance Modulus ◽  
Stellar Clusters ◽  
The Mean ◽  
The Difference

Aims. We demonstrate that reliable photometric distances of stellar clusters, and more generally of stars, can be obtained using pseudomagnitudes and rough spectral type without having to correct for visual absorption. Methods. We determine the mean absolute pseudomagnitude of all spectral (sub)types between B and K. Distances are computed from the difference between the star’s observed pseudomagnitude and its spectral type’s absolute pseudomagnitude. We compare the distances of 30 open clusters thus derived against the distances derived from TGAS parallaxes. Results. Our computed distances, up to distance modulus 12, agree within 0.1 mag rms with those obtained from TGAS parallaxes, proving excellent distance estimates. We show additionally that there are actually two markedly different distances in the cluster NGC 2264. Conclusions. We suggest that the pseudomagnitude distance estimation method, which is easy to perform, can be routinely used in all large-scale surveys where statistical distances on a set of stars, such as an open cluster, are required.

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