- ID:
- ivo://CDS.VizieR/J/A+AS/134/489
- Title:
- Be stars in MC young clusters
- Short Name:
- J/A+AS/134/489
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for Be stars in six fields centered on the young clusters NGC 330 and NGC 346 in the SMC, and NGC 1818, NGC 1948, NGC 2004 and NGC 2100 in the LMC. Be stars were identified by differencing R band and narrow-band H{alpha} CCD images. Our comparatively large images provide substantial Be star populations both within the clusters and in their surrounding fields. Magnitudes, positions and finding charts are given for the 224 Be stars found. The fraction of Be stars to normal B stars within each cluster is found to vary significantly although the average ratio is similar to the average Be to B star ratio found in the Galaxy. In some clusters, the Be star population is weighted to magnitudes near the main sequence turn-off. The Be stars are redder in V-I than normal main-sequence stars of similar magnitude and the redness increases with increasing H{alpha} emission strength.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/155/91
- Title:
- Be stars in open clusters with PTF/iPTF. I.
- Short Name:
- J/AJ/155/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We conducted a search for Be star candidates in open clusters using H{alpha} imaging photometry of the Palomar Transient Factory Survey to investigate some connections among Be star phenomena, cluster environments, and ages. Stellar members of clusters were identified by spatial distributions, near-infrared magnitudes and colors, and by proper motions. Among 104 open clusters, we identified 96 Be star candidates in 32 clusters; 11 of our candidates have been reported in previous studies. We found that the clusters with age 7.5<log(t(year))=<8.5 tend to have more Be star candidates; there is about a 40% occurrence rate within this age bin. The clusters in this age bin also tend to have a higher Be fraction N(Be)/N(Be+B-type). These results suggest that the environments of young and intermediate clusters are favorable to the formation of Be phenomena. Spatial distribution of Be star candidates with different ages implies that they do not form preferentially in the central regions. Furthermore, we showed that the mid-infrared (MIR) colors of the Be star candidates are similar to known Be stars, which could be caused by free-free emission or bound-free emission. Some Be star candidates might have no circumstellar dust according to their MIR colors. Finally, among 96 Be candidates, we discovered that one Be star candidate FSR 0904-1 exhibits long-term variability on the timescale of ~2000 days with an amplitude of 0.2-0.3 mag, indicating a long timescale of disk evolution.
- ID:
- ivo://CDS.VizieR/J/A+A/613/A70
- Title:
- Be stars in the exofield of CoRoT. II.
- Short Name:
- J/A+A/613/A70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The class of Be stars are the epitome of rapid rotators in the main sequence. These stars are privileged candidates for studying the incidence of rotation on the stellar internal structure and on non-radial pulsations. Pulsations are considered possible mechanisms to trigger mass-ejection phenomena required to build up the circumstellar disks of Be stars. Time series analyses of the light curves of 15 faint Be stars observed with the CoRoT satellite were performed to obtain the distribution of non-radial pulsation (NRP) frequencies in their power spectra at epochs with and without light outbursts and to discriminate pulsations from rotation-related photometric variations. Standard Fourier techniques were employed to analyze the CoRoT light curves. Fundamental parameters corrected for rapid-rotation effects were used to study the power spectrum as a function of the stellar location in the instability domains of the Hertzsprung-Russell (H-R) diagram. Frequencies are concentrated in separate groups as predicted for g-modes in rapid B-type rotators, except for the two stars that are outside the H-R instability domain. In five objects the variations in the power spectrum are correlated with the time-dependent outbursts characteristics. Time-frequency analysis showed that during the outbursts the amplitudes of stable main frequencies within 0.03c/d intervals strongly change, while transients and/or frequencies of low amplitude appear separated or not separated from the stellar frequencies. The frequency patterns and activities depend on evolution phases: i) the average separations between groups of frequencies are larger in the zero-age main sequence (ZAMS) than in the terminal age main sequence (TAMS) and are the largest in the middle of the MS phase; ii) a poor frequency spectrum with f<1c/d of low amplitude characterizes the stars beyond the TAMS; and iii) outbursts are seen in stars hotter than B4 spectral type and in the second half of the MS. The two main frequency groups are separated by {delta}f=(1.24+/-0.28).f_{rot}_ in agreement with models of prograde sectoral g-modes (m=-1,-2) of intermediate-mass rapid rotators. The changes of amplitudes of individual frequencies and the presence of transients correlated with the outburst events deserve further studies of physical conditions in the subatmospheric layers to establish the relationship between pulsations and sporadic mass-ejection events.
- ID:
- ivo://CDS.VizieR/J/A+A/290/609
- Title:
- Be stars near-IR excess
- Short Name:
- J/A+A/290/609
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+AS/119/271
- Title:
- Be stars uvby{beta} photometry
- Short Name:
- J/A+AS/119/271
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present uvby{beta} photometry for Be stars in eight open clusters and two OB associations. It is shown that Be stars occupy anomalous positions in the photometric diagrams, which can be explained in terms of the circumstellar continuum radiation contribution to the photometric indices. In the (b-y)_0_-M_V_ plane Be stars appear redder than the non emission B stars, due to the additional reddening caused by the hydrogen free-bound and free-free recombination in the circumstellar envelope. In the c_0_-M_V_ plane the earlier Be stars present lower c_0_ values than absorption-line B stars, which is caused by emission in the Balmer discontinuity, while the later Be stars deviate towards higher c_0_ values, indicating absorption in the Balmer discontinuity of circumstellar origin.
- ID:
- ivo://CDS.VizieR/J/A+A/335/565
- Title:
- Be stars variability
- Short Name:
- J/A+A/335/565
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The high accuracy and the homogeneity of Hipparcos data for bright stars have allowed us to quantify the degree of variability of Be stars. This degree has been found to be highly dependent on the temperature of the star. Rapid variability is the main feature of the 86% of early Be and less than 20% of late Be stars taking into account the limit of detection considered. In addition to Be stars reported in the Hipparcos catalogue (ESA 1997, Cat. <I/239>) as short-period variables, we have been able to enlarge the number of detections as well as to confirm periods previously determined. Be stars that show larger amplitude rapid variations are proposed as candidates for a search of multiperiodicity i.e. as non-radial pulsators. We have also searched for the presence of outbursts and fading events in the Hipparcos data. Outbursts have been frequently and preferentially detected in early Be stars with rather low to moderate v sini while fading events seem to be more conspicuous in stars with higher v sini. Mid-term and long-term variations have also been investigated. Several stars have shown some evidence of temporary quasi-periodic oscillations ranging between 10 and 200 days. Finally information concerning long-term variations is reported. Cycles shorter than or equal to the Hipparcos mission have mainly been detected in stars earlier than B6. Long-term time scales of late Be stars are confirmed to be longer by far.
- ID:
- ivo://CDS.VizieR/J/A+A/561/A8
- Title:
- Binary central stars of SMC PNe
- Short Name:
- J/A+A/561/A8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Optical Gravitational Lensing Experiment (OGLE), originally designed to search for microlensing events, provides a rich and uniform data set suitable for studying the variability of certain types of objects. We used the OGLE data to study the photometry of central stars of planetary nebulae (PNe) in the Small Magellanic Cloud (SMC). In particular, we searched for close binary central stars with the aim to constrain the binary fraction and period distribution in the SMC. We also searched for PNe mimics and removed them from the PNe sample. We identified 52 counterparts of PNe in the SMC in the I-band images from the OGLE-II and OGLE-III surveys. We analysed the time-series photometry of the PNe. Spectra of the photometric variables were obtained to constrain the nature of the objects or search for additional evidence for binarity. Eight variables were found. Of these, seven objects are PNe mimics, including one symbiotic star candidate. One close binary central star of PN with a period of 1.15 or 2.31 day was discovered. The obtained binary fraction for the SMC PNe and the observational biases are discussed in terms of the OGLE observations.
- ID:
- ivo://CDS.VizieR/J/A+A/459/137
- Title:
- Bright Be shell stars
- Short Name:
- J/A+A/459/137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Echelle observations are presented and discussed for 23 of the 27 known "normal" shell stars brighter than about 6.5mag. In addition to those typical cases, three stars with known transitions between emission & shell and pure emission line appearance, and three rapidly rotating B stars without records of line emission (Bn stars) are added to the sample.
- ID:
- ivo://CDS.VizieR/J/MNRAS/361/1055
- Title:
- BVI photometry of LMC Be stars
- Short Name:
- J/MNRAS/361/1055
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalogue with coordinates and photometric data of 2446 Be star candidates in the Large Magellanic Cloud (LMC), based on a search of the OGLE II data base. The I-band light curves of these stars show outbursts in 24% of the sample (Type-1 stars), high and low states in 10%, periodic variations in 6% (Type-3 stars), and stochastic variations in 60% of the cases. We report on the result of the statistical study of light curves of Type-1 and Type-3 stars in the LMC, and the comparison with the previously reported results of the Small Magellanic Cloud (SMC) sample.
- ID:
- ivo://CDS.VizieR/J/ApJ/760/10
- Title:
- BV light curves of {gamma} Cas (1997-2011)
- Short Name:
- J/ApJ/760/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The B0.5 IVe star {gamma} Cas is of great interest because it is the prototype of a small group of classical Be stars having hard X-ray emission of unknown origin. We discuss results from ongoing B and V observations of the {gamma} Cas star-disk system acquired with an Automated Photometric Telescope during the observing seasons 1997-2011. In an earlier study, Smith, Henry, & Vishniac (Cat. J/ApJ/647/1375) showed that light variations in {gamma} Cas are dominated by a series of comparatively prominent cycles with amplitudes of 0.02-0.03mag and lengths of 2-3 months, superimposed on a 1.21 day periodic signal some five times smaller, which they attributed to rotation. The cycle lengths clustered around 70 days, with a total range of 50-91 days. Changes in both cycle length and amplitude were observed from year to year. These authors also found the V-band cycles to be 30%-40% larger than the B-band cycles. In the present study, we find continued evidence for these variability patterns and for the bimodal distribution of the {Delta}B/{Delta}V amplitude ratios in the long cycles. During the 2010 observing season, {gamma} Cas underwent a mass-loss event ("outburst"), as evidenced by the brightening and reddening seen in our new photometry. This episode coincided with a waning of the amplitude in the ongoing cycle. The Be outburst ended the following year, and the light-curve amplitude returned to pre-outburst levels. This behavior reinforces the interpretation that cycles arise from a global disk instability. We have determined a more precise value of the rotation period, 1.215811+/-0.000030 days, using the longer 15-season data set and combining solutions from the V and B light curves. Remarkably, we also find that both the amplitude and the asymmetry of the rotational waveform changed over the years. We review arguments for this modulation arising from transits of a surface magnetic disturbance. Finally, to a limit of 5 mmag, we find no evidence for any photometric variation corresponding to the {gamma} Cas binary period, 203.55 days, or to the first few harmonics.
