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Long-term photometric observations of pre-main sequence objects in the field of North America/Pelican Nebula
摘要： To broaden the search and study stars in the early evolutionary phase, we investigated a sample of 17 pre-main sequence objects previously detected as either Hα emission-line pre-main sequence stars or T Tauri variables located in the field of the North America/Pelican Nebula complex. Johnson-Cousins B, V, Rc, Ic magnitudes and mean color indices for the program stars are determined from more than 12 400 measurements from archive photographic plates and from CCD data collected at 7 observatories covering the period of almost 60 years from 1954 up to 2013. We complemented previously rare insights on the photometry of the program stars and presented their photometric history, which for almost all program stars is the first long term photometric monitoring on a timescale of 6 decades. Eight program stars are found to be classical T Tauri stars of variability type II, while 6 program stars are weak-line T Tauri stars of variability type I. For the first time, periodicity is found for three stars: V1716 Cyg indicates a 4.15 day period, V2051 Cyg indicates a 384 day period, and V521 Cyg a period of 503 days.
关键词： stars: pre-main sequence,stars: variables: general
更新于2025-09-23 15:22:29
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Synthetic photometry for carbon-rich giants
摘要： Context. The evolution and spectral properties of stars on the asymptotic giant branch (AGB) are significantly affected by mass loss through dusty stellar winds. Dynamic atmosphere and wind models are an essential tool for studying these evolved stars, both individually and as members of stellar populations, to understand their contribution to the integrated light and chemical evolution of galaxies. Aims. This paper is part of a series with the purpose of testing state-of-the-art atmosphere and wind models of C-type AGB stars against observations, and making them available to the community for use in various theoretical and observational studies. Methods. We have computed low-resolution spectra and photometry (in the wavelength range 0.35–25 μm) for a grid of 540 dynamic models with stellar parameters typical of solar-metallicity C-rich AGB stars and with a range of pulsation amplitudes. The models cover the dynamic atmosphere and dusty outflow (if present), assuming spherical symmetry, and taking opacities of gas-phase species and dust grains consistently into account. To characterize the time-dependent dynamic and photometric behaviour of the models in a concise way we defined a number of classes for models with and without winds. Results. Comparisons with observed data in general show a quite satisfactory agreement for example regarding mass-loss rates vs. (J ? K) colours or K magnitudes vs. (J ? K) colours. Some exceptions from the good overall agreement, however, are found and attributed to the range of input parameters (e.g. relatively high carbon excesses) or intrinsic model assumptions (e.g. small particle limit for grain opacities). Conclusions. While current results indicate that some changes in model assumptions and parameter ranges should be made in the future to bring certain synthetic observables into better agreement with observations, it seems unlikely that these pending improvements will significantly affect the mass-loss rates of the models.
关键词： stars: carbon,stars: mass-loss,stars: AGB and post-AGB,stars: atmospheres,circumstellar matter,stars: variables: general
更新于2025-09-23 15:21:21
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A new method to identify subclasses among AGB stars using <i>Gaia</i> and 2MASS photometry
摘要： Aims. We explore the wealth of high-quality photometric data provided by data release 2 (DR2) of the Gaia mission for long-period variables (LPVs) in the Large Magellanic Cloud (LMC). Our goal is to identify stars of various types and masses along the asymptotic giant branch. Methods. For this endeavour, we developed a new multi-band approach combining Wesenheit functions WRP,BP?RP and WKs,J?Ks in the Gaia BP, RP, and 2MASS J, Ks spectral ranges, respectively, and use a new diagram, (WRP,BP?RP ? WKs,J?Ks ) versus Ks, to distinguish between di?erent kinds of stars in our sample of LPVs. We used stellar population synthesis models to validate our approach. Results. We demonstrate the ability of the new diagram to discriminate between O- and C-rich objects, and to identify low-mass, intermediate-mass, and massive O-rich red giants, as well as extreme C-rich stars. Stellar evolution and population synthesis models guide the interpretation of the results, highlighting the diagnostic power of the new tool to discriminate between stellar initial masses, chemical properties, and evolutionary stages.
关键词： stars: evolution,Magellanic Clouds,stars: AGB and post-AGB,stars: variables: general
更新于2025-09-23 15:21:21
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INITIAL FOLLOW-UP OF OPTICAL TRANSIENTS WITH COLORES USING THE BOOTES NETWORK
摘要： The Burst Observer and Optical Transient Exploring System (BOOTES) is a network of telescopes that allows the continuous monitoring of transient astrophysical sources. It was originally devoted to the study of the optical emission from gamma-ray bursts (GRBs) that occur in the Universe. In this paper we show the initial results obtained using the spectrograph COLORES (mounted on BOOTES-2), when observing optical transients (OTs) of diverse nature.
关键词： stars: variables: general,gamma-ray burst: general,Telescopes
更新于2025-09-11 14:15:04
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Mode identification based on time-series spectrophotometry for the bright rapid sdB pulsator EC 01541?1409
摘要： We present an analysis of time-resolved spectrophotometry gathered with FORS/VLT for the rapidly pulsating hot B subdwarf EC 01541?1409 with the aim of identifying the degree index (cid:2) of the larger amplitude modes. This mode identi?cation can be extremely useful in detailed searches for viable asteroseismic models in parameter space, and can be crucial for testing the validity of a solution a posteriori. To achieve it, we exploit the (cid:2)-dependence of the monochromatic amplitude, phase, and velocity-to-amplitude ratio of a mode as a function of wavelength. We use the (cid:2)-sensitive phase lag between the ?ux perturbation and the radial velocity as an additional diagnostic tool. On this basis, we are able to unambiguously identify the dominant 140.5 s pulsation of our target as a radial mode, and the second-highest amplitude periodicity at 145.8 s as an (cid:2) = 2 mode. We further exploit the exceptionally high-sensitivity data that we gathered for the dominant mode to infer modal properties that are usually quite di?cult to estimate in sdB pulsators, namely the physical values of the dimensionless radius, temperature, and surface gravity perturbations.
关键词： stars: oscillations,stars: individual: EC 01541-1409,techniques: imaging spectroscopy,stars: atmospheres,stars: variables: general,asteroseismology
更新于2025-09-10 09:29:36
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Detecting non-uniform period spacings in the <i>Kepler</i> photometry of <i>γ</i> Doradus stars: methodology and case studies
摘要： Context. The analysis of stellar oscillations is one of the most reliable ways to probe stellar interiors. Recent space missions such as Kepler have provided us with an opportunity to study these oscillations with unprecedented detail. For many multi-periodic pulsators such as γ Doradus stars, this led to the detection of dozens to hundreds of oscillation frequencies that could not be found from ground-based observations. Aims. We aim to detect non-uniform period spacings in the Fourier spectra of a sample of γ Doradus stars observed by Kepler. Such detection is complicated by both the large number of signi?cant frequencies in the space photometry and by overlapping non-equidistant rotationally split multiplets. Methods. Guided by theoretical properties of gravity-mode oscillation of γ Doradus stars, we developed a period-spacing detection method and applied it to Kepler observations of a few stars, after having tested the performance from simulations. Results. The application of the technique resulted in the clear detection of non-uniform period spacing series for three out of the ?ve treated Kepler targets. Disadvantages of the technique are also discussed, and include the disability to distinguish between di?erent values of the spherical degree and azimuthal order of the oscillation modes without additional theoretical modelling. Conclusions. Despite the shortcomings, the method is shown to allow solid detections of period spacings for γ Doradus stars, which will allow future asteroseismic analyses of these stars.
关键词： stars: fundamental parameters,asteroseismology,stars: variables: general,methods: data analysis
更新于2025-09-10 09:29:36
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Studying bright variable stars with the Multi-site All-Sky CAmeRA (MASCARA)
摘要： Context. The Multi-site All-Sky CAmeRA (MASCARA) aims to find the brightest transiting planet systems by monitoring the full sky at magnitudes 4 < V < 8.4, taking data every 6.4 s. The northern station has been operational on La Palma since February 2015. These data can also be used for other scientific purposes, such as the study of variable stars. Aims. In this paper we aim to assess the value of MASCARA data for studying variable stars by determining to what extent known variable stars can be recovered and characterised, and how well new, unknown variables can be discovered. Methods. We used the first 14 months of MASCARA data, consisting of the light curves of 53 401 stars with up to one million flux points per object. All stars were cross-matched with the VSX catalogue to identify known variables. The MASCARA light curves were searched for periodic flux variability using generalised Lomb–Scargle periodograms. If significant variability of a known variable was detected, the found period and amplitude were compared with those listed in the VSX database. If no previous record of variability was found, the data were phase folded to attempt a classification. Results. Of the 1919 known variable stars in the MASCARA sample with periods 0.1 < P < 10 days, amplitudes >2%, and that have more than 80 h of data, 93.5% are recovered. In addition, the periods of 210 stars without a previous VSX record were determined, and 282 candidate variable stars were newly identified. We also investigated whether second order variability effects could be identified. The O’Connell effect is seen in seven eclipsing binaries, of which two have no previous record of this effect. Conclusions. MASCARA data are very well suited to study known variable stars. They also serve as a powerful means to find new variables among the brightest stars in the sky. Follow-up is required to ensure that the observed variability does not originate from faint background objects.
关键词： stars: variables: general,stars: variables: Cepheids,binaries: eclipsing
更新于2025-09-04 15:30:14