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An Investigation of Short-Period Variable Stars. II. The AI Velorum Stars

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1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
1969ApJS...18..195B
... Two subgroups of δ Scuti stars were suggested. The stars in one group had a mass of 1.9 M ⊙ (Bessell, 1969a), while the mass of the stars in the other group was 0.5 M ⊙ (Bessell, 1969b). However, the future will show that this was not the final grouping of δ Scuti stars. ...
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Scientific research is a continuous process, and the speed of future progress can be estimated by the pace of finding explanations for previous research questions. In this observer's based view of stellar pulsation and asteroseismology, we start with the earliest observations of variable stars and the techniques used to observe them. The earliest variable stars were large amplitude, radial pulsators but were followed by other classes of pulsating stars. As the field matured, we outline some cornerstones of research into pulsating star research with an emphasis on changes in observational techniques. Improvements from photographs, to photometry, CCDs, and space telescopes allowed researchers to separate out pulsating stars from other stars with light variations, recognize radial and non-radial pulsation courtesy of increased measurement precision, and then use non-radial pulsations to look inside the stars, which cannot be done any other way. We follow several highlighted problems to show that even with excellent space data, there still may not be quick theoretical explanations. As the result of technical changes, the structure of international organizations devoted to pulsating stars has changed, and an increasing number of conferences specialized to space missions or themes are held. Although there are still many unsolved problems, such as mode identification in non-asymptotic pulsating stars, the large amount of data with unprecedented precision provided by space missions (MOST, CoRoT, Kepler) and upcoming missions allow us to use asteroseismology to its full potential. However, the enormous flow of data will require new techniques to extract the science before the next missions. The future of asteroseismology will be successful if we learn from the past and improve with improved techniques, space missions, and a properly educated new generation.
... These stars can exhibit large numbers of simultaneous oscillation modes (Breger et al. 2005;Catelan & Smith 2015, and references therein). Generally, δ Scutis are divided into two groups: high-amplitude δ Scutis (HADS, or AI Velorum stars: Bessell 1969) with amplitudes greater than ∼0.1 mag (Alcock et al. 2000), and low-amplitude δ Scutis (LADS) with smaller amplitudes. In Fig. 24, we plot an example of a HADS. ...
Article
Here we present the results from our analysis of six years of optical photometry taken by the Siding Spring Survey (SSS). This completes a search for periodic variable stars within the 30,000 square degrees of the sky covered by the Catalina Surveys. The current analysis covers 81 million sources with declinations between -20 and -75 degrees with median magnitudes in the range 11 < V < 19.5. We find approximately 34,000 new periodic variable stars in addition to the ∼9,000 RR Lyrae that we previously discovered in SSS data. This brings the total number of periodic variables identified in Catalina data to ∼110,000. The new SSS periodic variable stars mainly consist of eclipsing binaries, RR Lyrae, LPVs, RS CVn stars, δ Scutis and Anomalous Cepheids. By cross-matching these variable stars with those from prior surveys, we find that ∼90% of the sources are new discoveries and recover ∼95% of the known periodic variables in the survey region. For the known sources, we find excellent agreement between our catalogue and prior values of luminosity, period and amplitude. However, we find many variable stars that had previously been misclassified. Examining the distribution of RR Lyrae, we find a population associated with the Large Magellanic Cloud (LMC) that extends more than 20 degrees from its center confirming recent evidence for the existence of a very extended stellar halo in the LMC. By combining SSS photometry with Dark Energy Survey data, we identify additional LMC halo RR Lyrae, thus confirming the significance of the population.
... However, no general consensus has been reached yet on their evolutionary and pulsation properties. The names suggested in the literature range from SX Phoenicis (Nemec & Mateo 1990) to Dwarf Cepheids (Mateo et al. 1998;Vivas & Mateo 2013) to ultra-short-period Cepheids (Eggen 1979) to AI Velorum stars (Bessell 1969) to high-amplitude δ Scuti stars (McNamara 1995;Hog & Petersen 1997). The most relevant point concerning the classification is that SX Phe are considered the metal-poor extension of the classical δ Scuti stars. ...
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We present new multi-band (UBVI) time-series data of helium burning variables in the Carina dwarf spheroidal galaxy. The current sample includes 92 RR Lyrae-six of them are new identifications-and 20 Anomalous Cepheids, one of which is new identification. The analysis of the Bailey diagram shows that the luminosity amplitude of the first overtone component in double-mode variables is located along the long-period tail of regular first overtone variables, while the fundamental component is located along the short-period tale of regular fundamental variables. This evidence further supports the transitional nature of these objects. Moreover, the distribution of Carina double-mode variables in the Petersen diagram (P_1/P_0 vs P_0) is similar to metal-poor globulars (M15, M68), to the dwarf spheroidal Draco and to the Galactic Halo. This suggests that the Carina old stellar population is metal-poor and affected by a small spread in metallicity. We use trigonometric parallaxes for five field RR Lyrae stars to provide an independent estimate of the Carina distance using the observed reddening free Period--Wesenheit [PW, (BV)] relation. Theory and observations indicate that this diagnostic is independent of metallicity. We found a true distance modulus of \mu=20.01\pm0.02 (standard error of the mean) \pm0.05 (standard deviation) mag. We also provided independent estimates of the Carina true distance modulus using four predicted PW relations (BV, BI, VI, BVI) and we found: \mu=(20.08\pm0.007\pm0.07) mag, \mu=(20.06\pm0.006\pm0.06) mag, \mu=(20.07\pm0.008\pm0.08) mag and \mu=(20.06\pm0.006\pm0.06) mag. Finally, we identified more than 100 new SX Phoenicis stars that together with those already known in the literature (340) make Carina a fundamental laboratory to constrain the evolutionary and pulsation properties of these transitional variables.
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Summary This document is part of Subvolume B ‘Stars and Star Clusters’ of Volume 2 ‘Astronomy and Astrophysics’ of Landolt-Börnstein - Group VI Astronomy and Astrophysics.
Chapter
Summary This document is part of Subvolume B ‘Stars and Star Clusters’ of Volume 2 ‘Astronomy and Astrophysics’ of Landolt-Börnstein - Group VI Astronomy and Astrophysics.
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Arguments are presented that the AI Velorum variables are about 0.2 M ⊙ objects evolving with a roughly constant luminosity toward the white dwarf stage.
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It is widely accepted that pulsating variables with periods less than 0.2 day fall into two distinct groups. These defined by Kukarkin et al. (1969) as, firstly, RRs:RR Lyrae type variables with the period not exceeding 0 d . 21 (dwarf Cepheids). Belong to the population of the disk, are absent in clusters. Their luminosity is 2 m –3 m fainter than the luminosity of RRab and RRc stars. A typical representative – SX Phe. and secondly, δSct:δScuti type stars. Pulsating variables of spectral class A (late sub-classes) and F, the amplitudes of light variation do not exceed, as a rule, 0 m .1 (rarely up to 0 m .3). The form of light curve strongly varies usually. According to many characteristics resemble dwarf Cepheids, but differ from them by the small amplitudes. Are met in the Hyades-type clusters. Similar to the RRs type stars their periods do not exceed 0 d .2. A typical representative – δSct.
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Theoretical problems in connection with δ Sct and RRs type variables are reviewed. All evidence shows that δ Sct stars are normal main-sequence or early post main-sequence stars. Results of linear stability analyses of δ Sct models agree well with observations, the presence of non-variables in the strip being understandable in terms of helium diffusion. Excitation of non-radial modes may also occur; comparison of observed multiple periodicities with the theoretically derived period patterns for radial and non-radial modes is discussed as a means to distinguish between these possibilities. It is not known whether RRs variables are of the same nature as δ Sct stars or in a late evolutionary state with low mass. RRs variables pulsate in radial modes, and recent linear stability analyses seem to agree well with observations for both normal and low masses. The reason for the difference in amplitude between RRs and δ Sct stars is not known. Non-linear investigations may provide important information in the near future. The observed period ratios of RRs variables indicate for most of the double mode pulsators a slight deficiency in heavy elements and a normal mass; but more detailed investigations of this problem are needed.
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The variability of the dwarf cepheid VX Hya has been investigated during three nights using the uvby and beta filters. An average effective surface gravity of log g = 3.47 and an average surface temperature of 7000 K were found. The mean metallicity index of +0.003 magnitude indicates solar-type abundances. No evidence for a low-mass nature of this star is found from the metal abundance, period-gravity relation, and space motion. It is suggested that VX Hya is a large-amplitude delta Scuti star. Model-atmosphere calibrations of the uvby-beta indices using Kurucz's (1975) models and Breger's (1974) normalization are given.
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Proposed evolutionary models of AI Velorum variables are reviewed, and further arguments are offered that these variables are about 0.2 solar mass stars evolving with a roughly constant luminosity toward the white dwarf stage after having lost most of their mass during the red giant phase. Such pre-white-dwarf configurations contain most of their mass in a degenerate helium core, but their luminosity is due almost exclusively to shell hydrogen burning.
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From Broglia's and Pestarino's photoeletric and Balazs's photographic observations the star is found to have a beat period of 0,316330d, or in units of the primary period 3,397. This is the same value as that for AI Velorum obtained by Walraven.
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Recommended for spectrographic and photoelectric observations are the two variables of Beta Lyrae type, EP Lyrae and HP Lyrae. Both objects have been formerly classified as RV Tauri type stars according to their periods when no spectrographic observations were available. Objective prism plates taken with the Sonneberg 50/70/172 cm Schmidt telescope revealed the early supergiant spectral types of both stars.