Stars are an important part of the universe, and they considered the “engines” of cosmic evolution, because they create all the elements heavier than hydrogen and helium—the very elements that make ...up
us
and the world we live in. While the brightness of most stars appears steady, by using telescopes or even binoculars the brightness of some stars can be seen to change. These are called variable stars. Researching variable stars is important because the information from these stars helps scientists to understand the properties of
all
stars as well as the nature of the universe. This article will explain what variable stars are, what we can learn from them, and how even non-professionals, including
you
, can help to collect data on variable stars that might help astronomers to better understand our universe.
We obtained high temporal resolution spectroscopy of the unusual binary system AR Scorpii (AR Sco) covering nearly an orbit. The H emission shows a complex line structure similar to that seen in some ...polars during quiescence. Such emission is thought to be due to long-lived prominences originating on the red dwarf. A difference between AR Sco and these other systems is that the white dwarf (WD) in AR Sco is rapidly spinning relative to the orbital period. "Slingshot" prominences stable at 3 to 5 stellar radii require surface magnetic fields between 100 and 500 G. This is comparable to the estimated WD magnetic field strength near the surface of the secondary. Our time-resolved spectra also show emission fluxes, line equivalent widths, and continuum color varying over the orbit and the beat/spin periods of the system. During much of the orbit, the optical spectral variations are consistent with synchrotron emission with the highest energy electrons cooling between pulses. On the timescale of the beat/spin period we detect red- and blueshifted H emission flashes that reach velocities of 700 km s−1. Redshifted Balmer-emission flashes are correlated with the bright phases of the continuum beat pulses while blueshifted flashes appear to prefer the time of minimum in the beat light curve. We propose that much of the energy generated in AR Sco comes from fast magnetic reconnection events occurring near the inward face of the secondary and we show that the energy generated by magnetic reconnection can account for the observed excess luminosity from the system.
The Kilodegree Extremely Little Telescope (KELT) has been surveying more than 70% of the celestial sphere for nearly a decade. While the primary science goal of the survey is the discovery of ...transiting, large-radii planets around bright host stars, the survey has collected more than 106 images, with a typical cadence between 10-30 minutes, for more than four million sources with apparent visual magnitudes in the approximate range . Here, we provide a catalog of 52,741 objects showing significant large-amplitude fluctuations likely caused by stellar variability, as well as 62,229 objects identified with likely stellar rotation periods. The detected variability ranges in rms-amplitude from ∼3 mmag to ∼2.3 mag, and the detected periods range from ∼0.1 to 2000 days. We provide variability upper limits for all other ∼4,000,000 sources. These upper limits are principally a function of stellar brightness, but we achieve typical 1 sensitivity on 30 min timescales down to ∼5 mmag at , and down to ∼43 mmag at . We have matched our catalog to the TESS Input catalog and the AAVSO Variable Star Index to precipitate the follow-up and classification of each source. The catalog is maintained as a living database on the Filtergraph visualization portal at the URL https://filtergraph.com/kelt_vars.
Magnetic activity cycles are indirect traces of magnetic fields and can provide an insight on the nature and action of stellar dynamos and stellar magnetic activity. This, in turn, can determine ...local space weather and activity effects on stellar habitable zones. Using photometric monitoring of low-mass stars, we study the presence and properties of their magnetic activity cycles. We introduce long-term light curves of our sample stars, and discuss the properties of the observed trends, especially at spectral types where stars are fully convective (later than M3).
Issue Title: Papers from the 11th European Workshop on Astrobiology "Planets and Life: Evolution and Distribution" 11-14 July 2011, Köln, Germany Magnetic activity cycles are indirect traces of ...magnetic fields and can provide an insight on the nature and action of stellar dynamos and stellar magnetic activity. This, in turn, can determine local space weather and activity effects on stellar habitable zones. Using photometric monitoring of low-mass stars, we study the presence and properties of their magnetic activity cycles. We introduce long-term light curves of our sample stars, and discuss the properties of the observed trends, especially at spectral types where stars are fully convective (later than M3).PUBLICATION ABSTRACT
We have discovered a large number of circular and elliptical shells at 24 Delta *mm around luminous central sources with MIPS on board the Spitzer Space Telescope. Our archival follow-up effort has ...revealed 90% of these circumstellar shells to be previously unknown. The majority of the shells is only visible at 24 Delta *mm, but many of the central stars are detected at multiple wavelengths from the mid- to the near-IR regime. The general lack of optical counterparts, however, indicates that these sources represent a population of highly obscured objects. We obtained optical and near-IR spectroscopic observations of the central stars and find most of these objects to be massive stars. In particular, we identify a large population of sources that we argue represents a narrow evolutionary phase, closely related or identical to the luminous blue variable stage of massive stellar evolution.
Although the identification of the progenitors of type Ia supernovae (SNeIa) remains controversial, it is generally accepted that they originate from binary star systems in which at least one ...component is a carbon-oxygen white dwarf (WD); those systems are grouped under the wide umbrella of cataclysmic variables. Current theories for SNeIa progenitors hold that, either via Roche lobe overflow of the companion or via a wind, the WD accumulates hydrogen or helium rich material which is then burned to C and O onto the WD's surface. However, the specifics of this scenario are far from being understood or defined, allowing for a wealth of theories fighting for attention and a dearth of observations to support them. I discuss the latest attempts to identify and study those controversial SNeIa progenitors. I also introduce the most promising progenitor in hand and I present observational diagnostics that can reveal more members of the category.
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