- ID:
- ivo://CDS.VizieR/J/AJ/141/120
- Title:
- P Cygni H{alpha} measurements
- Short Name:
- J/AJ/141/120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- P Cygni is a prototype of the luminous blue variables (or S Doradus variables), and the star displays photometric and emission line variability on a timescale of years (known as the "short S Doradus-phase" variations). Here we present new high-resolution H{alpha} spectroscopy of P Cyg that we combine with earlier spectra and concurrent V-band photometry to document the emission and continuum flux variations over a 24 year time span.
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- ID:
- ivo://CDS.VizieR/J/AJ/135/1624
- Title:
- PEARS emission-line galaxies
- Short Name:
- J/AJ/135/1624
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Hubble Space Telescope Advanced Camera for Surveys grism Probing Evolution And Reionization Spectroscopically (PEARS) survey provides a large dataset of low-resolution spectra from thousands of galaxies in the GOODS north and south fields. One important subset of objects in these data is emission-line galaxies (ELGs), and we have investigated several different methods aimed at systematically selecting these galaxies. Here, we present a new methodology and results of a search for these ELGs in the PEARS observations of the Hubble Ultra Deep Field (HUDF) using a 2D detection method that utilizes the observation that many emission lines originate from clumpy knots within galaxies. This 2D line-finding method proves to be useful in detecting emission lines from compact knots within galaxies that might not otherwise be detected using more traditional 1D line-finding techniques.
- ID:
- ivo://CDS.VizieR/J/AJ/141/64
- Title:
- PEARS emission-line galaxies spectroscopy
- Short Name:
- J/AJ/141/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present spectroscopy of 76 emission-line galaxies (ELGs) in Chandra Deep Field South taken with the LDSS3 spectrograph on the Magellan Telescope. These galaxies are selected because they have emission lines with the Advanced Camera for Surveys (ACS) grism data in the Hubble Space Telescope Probing Evolution and Reionization Spectroscopically (PEARS) grism Survey. The ACS grism spectra cover the wavelength range 6000-9700{AA} and most PEARS grism redshifts are based on a single emission line + photometric redshifts from broadband colors; the Magellan spectra cover a wavelength range from 4000{AA} to 9000{AA} and provide a check on redshifts derived from PEARS data.
- ID:
- ivo://CDS.VizieR/J/ApJ/863/151
- Title:
- Period analysis of 7 field RRab stars
- Short Name:
- J/ApJ/863/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the times of light maximum collected from the GEOS RR Lyrae database and determined from sky surveys, we utilize the O-C method to study the period variations of seven field ab-type RR Lyrae stars. The time coverage of data for most stars is more than 100 years, allowing us to investigate period changes over a large time span. We find that the O-C diagrams for most stars can be described by a combination of cyclic variations and long-term period changes. Assuming the former were caused by the light-travel-time effect, the pulsation and orbital parameters are obtained by the nonlinear fitting. We find that the orbital periods in our sample range from 33 to 78 years, and the eccentricities are relatively higher than the results for other candidates (e>0.6). The minimal masses of the potential companions of XX And, BK Dra, and RY Psc are less than one solar mass, and those of SV Eri, AR Her, and RU Scl are 3.3, 2.1, and 3.4M_{sun}_, respectively. Moreover, we suggest that the companion of AR Her may be a blue straggler that experienced mass transfer or a merger of two stars. The O-C diagram for ST Vir also shows distinct long- term period decrease, and in the O-C residuals, additional quasi-periodic variations that can be described by damped oscillation are found. Combining the data from the literature and our analysis, we plot the log P-AO-C diagram. The distribution of our binary candidates suggests that their period variations are not caused by the Blazhko effect.
- ID:
- ivo://CDS.VizieR/J/A+A/554/A108
- Title:
- Periodic variables in NGC 3766
- Short Name:
- J/A+A/554/A108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the population of periodic variable stars in the open cluster NGC3766 based on a 7-year multiband monitoring campaign conducted on the 1.2m Swiss Euler telescope at La Silla, Chili. The data reduction, light curve cleaning, and period search procedures, combined with the long observation time line, allowed us to detect variability amplitudes down to the mmag level. The variability properties were complemented with the positions in the color-magnitude and color-color diagrams to classify periodic variable stars into distinct variability types. We find a large population (36 stars) of new variable stars between the red edge of slowly pulsating B (SPB) stars and the blue edge of delta Sct stars, a region in the Hertzsprung-Russell (HR) diagram where no pulsation is predicted to occur based on standard stellar models. The bulk of their periods ranges from 0.1 to 0.7d, with amplitudes between 1 and 4mmag for the majority of them. About 20% of stars in that region of the HR diagram are found to be variable, but the number of members of this new group is expected to be higher, with amplitudes below our mmag detection limit. The properties of this new group of variable stars are summarized and arguments set forth in favor of a pulsation origin of the variability, with g-modes sustained by stellar rotation. Potential members of this new class of low-amplitude periodic (most probably pulsating) A and late-B variables in the literature are discussed. We additionally identify 16 eclipsing binary, 13 SPB, 14 delta Sct, and 12 gamma Dor candidates, as well as 72 fainter periodic variables. All are new discoveries. We encourage searching for this new class of variables in other young open clusters, especially in those hosting a rich population of Be stars.
- ID:
- ivo://CDS.VizieR/J/PASP/121/1188
- Title:
- Periodic variables in NGC 2301
- Short Name:
- J/PASP/121/1188
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for periodic variables within 4078 time-series light curves and an analysis of the period-color plane for stars in the field of the open cluster NGC 2301. One hundred thirty-eight periodic variables were discovered, of which five are eclipsing binary candidates with unequal minima. The remaining 133 periodic variables appear to consist mainly of late-type stars whose variation is due to rotation modulated by star spot activity. The determined periods range from less than a day to over 14 days and have nearly unreddened B-R colors in the range of 0.8 to 2.8. The Barnes (2003ApJ...586..464B) interpretation of the period-color plane of late type stars is tested with our data. Our data did not show distinct I and C sequences, likely due to nonmember field stars contaminating in the background, as we estimate the total contamination to be 43%. Using different assumptions, the gyrochronological age of the cluster is calculated to be 210+/-25Myr, which falls in the range of age values (164-250Myr) determined by previous studies. Finally, we present evidence which nullifies the earlier suggestion that two of the variable stars in NGC 2301 might be white dwarfs.
- ID:
- ivo://CDS.VizieR/J/ApJS/241/35
- Title:
- Period-luminosity relations of RSGs in M33 & M31
- Short Name:
- J/ApJS/241/35
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- Based on previously selected preliminary samples of red supergiants (RSGs) in M33 and M31, the foreground stars and luminous asymptotic giant branch stars are further excluded, which leads to the samples of 717 RSGs in M33 and 420 RSGs in M31. With the time-series data from the Intermediate Palomar Transient Factory survey spanning nearly 2000 days, the period and amplitude of RSGs are analyzed. According to the light-curve characteristics, they are classified into four categories in which 84 and 56 objects in M33 and M31, respectively, are semi-regular variables. For these semi-regular variables, the pulsation mode is identified by comparing with the theoretical model, which yielded 19 (7) sources in the first overtone mode in M33 (M31), and the other 65 (49) RSGs in M33 (M31) in the fundamental mode. The period-luminosity (P-L) relation is analyzed for the RSGs in the fundamental mode. The P-L relation is found to be tight in the infrared, i.e., the Two Mircon All-Sky Survey (2MASS) JHK_S_ bands and the short-wavelength bands of Spitzer. Meanwhile, the inhomogeneous extinction causes the P-L relation scattering in the V band, and the dust emission causes the less tight P-L relation in the Spitzer/[8.0] and [24] bands. The derived P-L relations in the 2MASS/K_S_ band are in agreement with those of RSGs in the Small Magellanic Cloud, the Large Magellanic Cloud, and the Milky Way within the uncertainty range. It is found that the number ratio of RSGs pulsating in the fundamental mode to the first overtone mode increases with metallicity.
- ID:
- ivo://CDS.VizieR/J/AJ/135/1459
- Title:
- Period of M15 variable stars
- Short Name:
- J/AJ/135/1459
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new BVI CCD photometry for variables in the globular cluster M15. Our photometry was obtained using both the image subtraction package ISIS and DAOPHOT/ALLFRAME. The data were acquired in 2001 on two observing runs on 11 observing nights using the 2m telescope of the Bulgarian National Astronomical Observatory "Rozhen" with a Photometrics CCD camera. For 39 previously known variables, we present a period for the first time, and improved periods were obtained for many previously known variables. Fourteen new variables are reported. We present updated Bailey diagrams for the cluster, and discuss its Oosterhoff classification. Although many of M15's RRab pulsators fall at an intermediate locus between Oosterhoff types I and II (OoII) in the Bailey diagram, we argue that M15 is indeed a bona fide OoII globular cluster.
- ID:
- ivo://CDS.VizieR/J/A+A/544/A28
- Title:
- Period variation in BW Vulpeculae redux
- Short Name:
- J/A+A/544/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For the past 25 years, BW Vulpeculae has been the topic of period analyses centered on a secular period change with a periodic variation superposed, presumed to be due to light time effects in a binary system. According to this paradigm, one would expect what seems like a period increase of about 0.5s during or soon after the year 2001. I have continued photometric monitoring through the year 2012, adding 40 new timings of maximum and minimum light. This expected change in period did not occur, which rules out that interpretation of the period variation. As of 2012, the observed timings are about two hours early compared to those predicted by the quadratic ephemeris, but are very close to those predicted by the linear ephemeris. In fact, the period has remained constant for the last 32 years, indicating that the previous epochs of constant period are almost certainly the correct interpretation, though the cause of the period changes is still not clear. Continued photometric monitoring of BW Vul leads to the conclusion that the period changes are abrupt, followed by epochs of constant period lasting between 12 and at least 32 years.
- ID:
- ivo://CDS.VizieR/J/AJ/154/217
- Title:
- Period variations for the Cepheid VZ Cyg
- Short Name:
- J/AJ/154/217
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Cepheid Period-Luminosity law is a key rung on the extragalactic distance ladder. However, numerous Cepheids are known to undergo period variations. Monitoring, refining, and understanding these period variations allows us to better determine the parameters of the Cepheids themselves and of the instability strip in which they reside, and to test models of stellar evolution. VZ Cyg, a classical Cepheid pulsating at ~4.864 days, has been observed for over 100 years. Combining data from literature observations, the Kilodegree Extremely Little Telescope (KELT) transit survey, and new targeted observations with the Robotically Controlled Telescope (RCT) at Kitt Peak, we find a period change rate of dP/dt=-0.0642+/-0.0018 s/yr. However, when only the recent observations are examined, we find a much higher period change rate of dP/dt=-0.0923+/-0.0110 s/yr. This higher rate could be due to an apparent long-term (P~26.5 years) cyclic period variation. The possible interpretations of this single Cepheid's complex period variations underscore both the need to regularly monitor pulsating variables and the important benefits that photometric surveys such as KELT can have on the field. Further monitoring of this interesting example of Cepheid variability is recommended to confirm and better understand the possible cyclic period variations. Further, Cepheid timing analyses are necessary to fully understand their current behaviors and parameters, as well as their evolutionary histories.
