AR Lacertae Research Articles

VLBI Astrometry of radio stars to link radio and optical celestial reference frames. I. HD 199178 & AR Lacertae

ABSTRACT To accurately link the radio and optical Celestial Reference Frames (CRFs) at optical bright end, i.e. with GaiaG-band magnitude $\lesssim$13, increasing number and improving sky distribution of radio stars with accurate astrometric parameters from both Very Long Baseline Interferometry (VLBI) and Gaia measurements are mandatory. We selected two radio stars HD 199178 and AR Lacertae as the target for a pilot program for the frame link, using the Very Long Baseline Array at 15 GHz at six epochs spanning about 1 yr, to measure their astrometric parameters. The measured parallax of HD 199178 is 8.949 ± 0.059 mas and the proper motion is μαcos δ = 26.393 ± 0.093 and μδ = −0.950 ± 0.083 mas yr−1, while the parallax of AR Lac is 23.459 ± 0.094 mas and the proper motion is μαcos δ = −51.906 ± 0.138 and μδ = 46.732 ± 0.131 mas yr−1. Our VLBI measured astrometric parameters have accuracies about 4–5 times better than the corresponding historic VLBI measurements and comparable accuracies with those from Gaia, validating the feasibility of frame link using radio stars. With the updated astrometric parameters for these two stars, there is a ∼25 per cent reduction of the uncertainties on the Y-axis for both orientation and spin parameters.

WDJ220838.73+454434.04: a White Dwarf Companion in the AR Lacertae System

We present WDJ220838.73+454434.04 (hereafter WD2208+454), a wide, co-moving white dwarf companion to the eclipsing binary system, AR Lacertae. The companion was discovered through the Backyard Worlds: Planet 9 citizen science collaboration. It has a separation of 21.″9 on the sky from the central eclipsing pair, translating to a projected separation of ∼930 au. We present a review of the physical properties and orbital parameters of this new addition to the system.

Extensive serendipitous X-ray coverage of a flare star with ROSAT

We report the serendipitous discovery of a flare star observed with the ROSAT X-ray observatory. From optical spectra, which show strong and variable emission lines of the hydrogen Balmer series and neutral helium, we classify this object as a M3.0Ve star, and estimate a distance of 52 pc from published photometry. Due to the star's close proximity (13.6') to the calibration source and RS CVn binary AR Lacertae, long term X-ray coverage is available in the ROSAT archive (~50 hours spanning 6.5 years). Two large flare events occurred early in the mission (6-7/1990), and the end of a third flare was detected in 6/1996. One flare, observed with the Position Sensitive Proportional Counter (PSPC), had a peak luminosity Lx=1.1x10^{30} erg/s, an e-folding rise time of 2.2 hours and a decay time of 7 hours. This decay time is one of the longest detected on a dMe star, providing evidence for the possibility of additional heating during the decay phase. A large HRI flare (peak Lx=2.9x10^{30} erg/s) is also studied. The "background" X-ray emission is also variable - evidence for low-level flaring or microflaring. We find that >=59% of the HRI counts and >=68% of the PSPC counts are due to flares. At least 41% of the HRI exposure time and 47% of the PSPC are affected by detectable flare enhancement.

Spectral imaging maps of AR Lacertae

In October 1994 the RS CVn eclipsing binary AR Lacertae was monitored by IUE during two orbital cycles. We have used 59 low resolution spectra, acquired in the range 1150-1950 A, to derive light curves for emission lines formed at different temperatures between about 10 000 and 200 000 K and to study the flare signatures versus temperature of line formation. We have analyzed a sequence of 59 high resolution Mgii k line profiles using multi-Gaussian fits (the spectral imaging technique) to derive information of the spatial structure of the chromospheres of both stars in the AR Lac system. We discuss the quiet chromospheric emission from both stars, and we show that enhanced Mgii emission is present in extended structures corotating with the K0 IV star and close to the system center-of-mass. We also report on evidence for absorbing structures toward both the stars. This study of AR Lac used the new orbital elements of Marino et al. ([CITE]) and spectra reduced and calibrated with NEWSIPS. A comparison between fluxes derived from the analyzed NEWSIPS spectra and from IUESIPS spectra is provided.

Subgiant luminosity excesses in eclipsing binary systems

It has been shown that radius and temperature excesses are largeat for subgiant stars in DS systems and low-mass and long-period SD systems, and smallest for subgiant stars in AR systems and lowmass and short-period SD systems. Subgiant stars in AR and more massive SD systems exhibit temperature deficiencies which are largest for the primaries of the AR systems. It is necessary to divide the class of SD systems into groups according to mass and orbital period while studying their properties. Investigations of subgiant stars from eclipsing binary systems have shown that they possess luminosity excesses for their masses. The excesses are determined as the difference between the observed subgiant luminosities and those of mainsequence stars with similar masses. Generally, an excess indicates that the subgiant does not follow the mass-luminosity relation. At the same time subgiants in some cases show luminosity excesses, and in other cases have radii excesses, which are inherent to detached subgiants of DS systems (Batten, 1976). Subgiant stars are present in three types of eclipsing binary stars. According to Svechnikov (1986) they can be companions in semi-detached systems (SD systems), in systems with a detached subgiant (DS systems) as well as primary and secondary stars in the eclipsing systems of AR Lacertae type (AR systems). In SD systems the subgiant completely fills up its Roche lobe, whereas in DS and AR systems the subgiant lies deep inside it. This testifies to the differences in subgiant star structure. Let us consider the problem of the origin of luminosity excesses calculating them for subgiant stars of different types of eclipsing binary systems and dividing them into the following components: a, radius excesses; b, temperature excesses. To calculate the excesses we used data on stars’ properties from Karetnikov and Andronov (1989); and from Karetnikov (1991) the averaged formulae of mass-radius and mass-temperature relations. We have also determined the correlations bf excesses with binary system size A, subgiant mass A4 aiid stellar mas ratio q.

Stellar plages

The solar surface contains of bright regions (plages) and dark regions (sunspots) superposed on the photosphere. If the solar analogy is valid, then active late-type stars should also exhibit bright, spatially distinct plages. These plages can be detected by rotational modulation of chromospheric flux, or by Doppler imaging in chromospheric/transition region lines. I review the evidence for the existence of plages, with particular emphasis on two very active systems: AR Lacertae, for which we have sequences of Doppler imaging observations since 1984, and AB Doradus, which we observed extensively in 1994. I conclude that we need to be cautious when relying on the solar analogy to interpret observations of the most active late-type stars.

Corona(e) of AR Lacertae. I. The Temperature and Abundance Distribution

view Abstract Citations (92) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Corona(e) of AR Lacertae. I. The Temperature and Abundance Distribution Singh, K. P. ; White, N. E. ; Drake, S. A. Abstract X-ray spectra of the RS CVn binary AR Lac, obtained from simultaneous observations with the ROSAT PSPC and the ASCA SIS and GIS detectors, have been analyzed to study the coronal temperature and abundance distribution. The spectra were jointly fitted with plasma emission models to the following possible temperature distributions: (a) one with discrete multitemperature emission components, (b) a continuous emission measure with a power-law dependence on temperature, and (c) a continuous emission distribution parameterized by the sum of a sixth-order Chebyshev polynomial. We find that (i) solar abundance plasma models with either discrete or continuous emission measure (CEM) distributions are rejected, (ii) the best fit is obtained with a two-temperature (2T) plasma emission model with an underabundance of the elements 0, Mg, Si, S, Ar, Ca, and Fe by a factor of 3-4 relative to the solar photospheric values, and (iii) the best-fit CEM distribution also has similarly reduced abundances but fits the data less well than the 2T model. These results are confirmed even when the Fe-L region, which is subject to uncertainties in the atomic physics, is excluded from the fit. We consider optical depth effects as unlikely to be the explanation for the observed weakness of the line complexes relative to the continuum. Analysis of the spectral data during the primary and secondary eclipses shows that the emission measure of the high-temperature component in the 2T models appears to be more affected by the primary eclipse than the low-temperature component, suggesting that part of the former is concentrated in structures that are spatially more compact. Publication: The Astrophysical Journal Pub Date: January 1996 DOI: 10.1086/176695 Bibcode: 1996ApJ...456..766S Keywords: STARS: BINARIES: ECLIPSING; STARS: ABUNDANCES; STARS: CORONAE; STARS: INDIVIDUAL CONSTELLATION NAME: AR LACERTAE; X-RAYS: STARS full text sources ADS | data products SIMBAD (5) HEASARC (1) Related Materials (1) Part 2: 1996ApJ...473..470S

Chromospheric emission line mapping

Throughout its eighteen years of operation, the International Ultraviolet Explorer has afforded us the opportunity to make many new discoveries regarding the nature of the outer atmospheres of magnetically active, late-type stars. High-resolution spectra obtained continuously throughout the rotational cycle of rapidly-rotating stars have been used to map the spatial structure of the magnetic active regions in stellar chromospheres. The RS CVn-type binary system AR Lacertae has been observed intensively at 3 epochs, with additional observations with less complete phase coverage was obtained at 4 other epochs. Taken together, we are able to probe the evolution of atmospheric structure of AR Lac over a 13-year timeline. I briefly review techniques of chromospheric emission line mapping, and I summarize the IUE results for AR Lac, V711 Tau, EI Eri, V1794 Cyg, and TY Pyx. I conclude with a description of chromospheric imaging programs (present and future) that make use of the Hubble Space Telescope.

Extreme Ultraviolet Explorer observations of the RS Canum Venaticorum systems AR Lacertae and II Pegasi

view Abstract Citations (8) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Extreme Ultraviolet Explorer Observations of the RS Canum Venaticorum Systems AR Lacertae and II Pegasi Patterer, R. J. ; Vedder, P. W. ; Jelinsky, P. ; Brown, A. ; Bowyer, S. Abstract We report observations of two RS CVn systems, II Peg and AR Lac, which were calibration targets during the in-orbit checkout phase of the Extreme Ultraviolet Explorer (EUVE). We have determined count rates, and, based on these count rates, preliminary emission measure analyses have been done. The Lexan/boron band count rates were 0.0849 +/- 0.0023 counts/s for AR Lac and 0.218 +/- 0.031 counts/s for II Peg during its quiescent state. Temperatures and emission measures derived from the EUVE data are consistent with previously published values. We also report a flare seen during the II Peg observations which has characteristics similar to previously observed flares on II Peg. During the flare the Lexan/boron count rate increased by at least a factor of 2.5, and the minimum total duration was about 34,000 s (about 9.4 hr). Publication: The Astrophysical Journal Pub Date: September 1993 DOI: 10.1086/186995 Bibcode: 1993ApJ...414L..57P Keywords: Eclipsing Binary Stars; Extreme Ultraviolet Explorer Satellite; G Stars; K Stars; Astronomical Satellites; Emission Spectra; Stellar Coronas; Stellar Flares; Astrophysics; STARS: CORONAE; STARS: INDIVIDUAL CONSTELLATION NAME: AR LACERTAE; STARS: INDIVIDUAL CONSTELLATION NAME: II PEGASI; STARS: LATE-TYPE full text sources ADS | data products SIMBAD (2) MAST (1)

A study of the spatial and spectral characteristics of the corona of AR Lacertae

X-ray observations of the eclipsing RS CVn binary AR Lac covering both primary and secondary minimum, obtained with the position sensitive proportional counter (PSPC) on-board ROSAT, are presented. The X-ray light curves clearly show a deep primary eclipse in all three PSPC spectral bandpasses covering the bands 0.1-0.28 keV, 0.4-1.1 keV, and 1.1-2.4 keV. A shallow secondary minimum occuring before phase 0.5 is seen in the total light curve. Phase-dependent spectral analysis is performed both with a two-temperature model as well as a hydrostatic loop model. During primary eclipse the emission measures of the low- and the high-temperature component drop, while the derived coronal temperatures show no orbital variation

A period study of AR Lacertae

view Abstract Citations (13) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Period Study of AR Lacertae Kim, Chun-Hwey Abstract Fifteen new times of minimum light are presented for AR Lac. Times of minimum light obtained between December 1982 and November 1986 confirm that the period of the system has decreased since the early 1960's. Three possible explanatory mechanisms are examined (abrupt changes of period due to mass transfer, a light-time effect due to a hypothetical third body, and anisotropic mass ejection), but none seem to explain the period variation. A conceptually new way of considering this variation. Publication: The Astronomical Journal Pub Date: November 1991 DOI: 10.1086/116001 Bibcode: 1991AJ....102.1784K Keywords: Eclipsing Binary Stars; Stellar Orbits; Variable Stars; Bl Lacertae Objects; Light Curve; Orbital Elements; Astronomy; STARS: ECLIPSING BINARIES; STARS: VARIABLES full text sources ADS | data products SIMBAD (6)

A study of unitary light curves of AR Lacertae

During the 1982 - 1983 season, the eclipsing binary AR Lac was observed photoelectrically with yellow and blue filters at Yonsei University Observatory. As has often happened, the light curves show changes in the depth of primary minimum and apparently extraneous distortion outside eclipses. Solutions on the Russell model were obtained; the geometric and photometric elements agree well with those of Chambliss (1976) and Park (1984).

Flare features of AR Lacertae

BV optical flares of AR Lacertae, found in 1979 observations, are presented and their features are discussed. The effect of wave migration and the significance levels of flares originating around both eclipses have been estimated. Flare features suggest that both the components of AR Lac have spotted regions and show activity. The varying amplitudes of flares indicate varying degrees of activity. These results are well supported by observations in other wavelength regions.

Wave minimum of AR Lacertae

U, B, andV observations of AR Lacertae, obtained in 1981, have been presented alongwith the colour indices. A distortion wave minimum is found to lie at 0 . 21. The amplitude of the wave minimum inV filter is too weak, while it is stronger inU andV filters, the strongest being inV filter. The period of the migration wave turns out to be 2.53 yr.

Hydrogen-alpha observations of RS Canum Venaticorum stars. III - The eclipsing systems AR Lacertae and SZ PISCIUM

view Abstract Citations (32) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hydrogen-alpha observations of RS Canum Venaticorum stars. III. The eclipsing systems AR Lacertae and SZ Piscium. Huenemoerder, D. P. ; Ramsey, L. W. Abstract The authors have spectroscopically monitored two eclipsing double-lined RS CVn binaries, AR Lacertae and SZ Piscium, over many orbital periods at the wavelength of Hα. Excess Hα emission profiles were derived by subtracting composite comparison spectra synthesized from observations of single inactive stars. AR Lac showed no excess Hα emission. SZ Psc was highly active with emission from the cooler stellar component. SZ Psc also underwent a large Hα outburst during and after which profiles were suggestive of a circumstellar origin. Publication: The Astronomical Journal Pub Date: April 1984 DOI: 10.1086/113547 Bibcode: 1984AJ.....89..549H Keywords: Eclipsing Binary Stars; H Alpha Line; Stellar Spectrophotometry; Emission Spectra; Solar Flares; Spectral Energy Distribution; Stellar Envelopes; Stellar Rotation; Stellar Temperature; Temporal Distribution; Astrophysics full text sources ADS | data products SIMBAD (3) Related Materials (2) Part 1: 1984AJ.....89..115R Part 3: 1985AJ.....90..499H

VLA observations of the eclipsing binary system AR Lacertae

view Abstract Citations (23) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS VLA observations of the eclipsing binary system AR Lacertae. Doiron, D. J. ; Mutel, R. L. Abstract Dual-frequency radio observations of the RS CVn binary system AR Lacertae are reported during two secondary eclipses. No clearly defined eclipse signature was observed during either eclipse at either 1.5 or 4.9 GHz. This implies a lower limit of 5×1011 cm for the source diameter if the source is located in the orbital plane. Significant circular polarization (2% - 8%) was observed on both days, with a helicity reversal between 1.5 and 4.9 GHz. This polarization signature is consistent with a gyro-synchrotron emission mechanism if the source becomes optically thick between 1.5 and 4.9 GHz. Using this emission model, the derived range of magnetic field strength is 5 ⪉ B ⪉ 80 G. Publication: The Astronomical Journal Pub Date: March 1984 DOI: 10.1086/113533 Bibcode: 1984AJ.....89..430D Keywords: Bremsstrahlung; Circular Polarization; Eclipsing Binary Stars; Light Curve; Radio Astronomy; Stellar Radiation; Synchrotron Radiation; X Ray Astronomy; Astrophysics full text sources ADS | data products SIMBAD (1)

First observations of stellar coronal structure - The coronae of AR Lacertae

In connection with the present investigation, X-ray, radio, and ultraviolet observations of AR Lacertae over one orbital cycle have been obtained. The X-ray light curve shows a deep primary minimum and a broad, shallow secondary minimum. The quiescent corona of the G2 IV component is small and asymmetric. This corona extends some 0.02 stellar radii above the photosphere; the leading, spotted hemisphere is brighter in X-rays than the trailing hemisphere. The K0 IV component has two coronal components. The extended, presumably hotter component extends to one stellar radius above the photosphere and exhibits a brighter leading hemisphere. There is an inner coronal component which is small relative to the stellar radius, but the lack of coverage past mid-eclipse severely limits the possibility to deduce the nature of this component. The UV observations also imply a nonuniform surface distribution of plage regions.

Coronal and Chromospheric Structure in AR Lac - II: Physical Characteristics of the Atmosphere

In this series of papers we report on an effort to deduce the morphology of the chromosphere and corona of AR Lacertae, an eclipsing RS CVn system (Hall 1976), via observations at UV, radio, and X-ray wavelengths during a complete orbital cycle. In another paper (Gibson, Walter and Basri 1982, Paper I), we present the observational data and general constraints on the morphology of the coronae. The full study will be published elsewhere (Walter, Gibson, and Basri 1982).

The light curve variations in AR Lacertae

The eclipsing binary AR Lac has been observed in two colours,B andV, in 1980 and 1981. The new times of minimal obtained during the observatons indicate that the period of the system is still continuing its decrease. The wave-like distortions outside eclipses have two maxima and are very similar in shape in successive two years.

Photoelectric elements of AR Lacertae

Geometrical elements of the system AR lacertae have been obtained and its colour has been discussed. The absolute dimensions have been obtained on the basis of the spectroscopic elements given by Sanford (1951). The primary component lies fairly close to the Main Sequence on the logm-log R plot and the secondary falls away from the Main Sequence. The values of the Roche constants indicate that AR Lacertae is a detached system.