Large Starspots Research Articles

A near‐contact binary: CN Andromedae

AbstractNew BVR light curves and photometric analysis of the eclipsing binary star CN And are presented. The shape of the light curves are typical of β Lyr type, and there are large asymmetries between maxima. The BVR light curves and the radial velocity curves (from Rucinski et al. 2000) were solved with the Wilson‐Devinney method, simultaneously. The results suggest that CN And is a almost contact binary system, in which the component stars are filling ∼99% of their Roche lobes. We discuss the model with a large dark starspot on the more massive star and a bright substellar spot on the companion to account for the light curve asymmetries. The absolute parameters of the system were also derived. The system resembles the near contact binary V1010 Oph according to its Roche configuration and light curve asymmetries. We, also, discuss the evolution of the system: it seems to be in a transition phase to the contact era. All previous times of minimum light were collected and combined with the new ones presented in this work. The variation of the orbital period of the system was then analyzed. The results reveal that the orbital period has a secular decrease of about 1.98 ± 0.04 sec per century, which corresponds to a conservative mass transfer from the more to the less massive component at a rate of (1.52 ± 0.09) × 10–7 m⊙/yr or a mass loss from the primary component due to magnetic stellar winds at a rate of (7.83 ± 0.09) × 10–8 m⊙/yr. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High-Resolution Spectroscopy of some Active Southern Stars

High-resolution échelle spectra of 42 nearby southern solar-type stars have been obtained, in a search for young, single, active, and rapidly rotating sun-like stars suitable for Doppler imaging and Zeeman Doppler imaging studies. As a result of this survey, 13 stars were determined to be youthful with ages less than 600 Myr (Hyades age) and eight of these were found to have projected rotational velocities in excess of 15 km s−1. In addition, five spectroscopic binary systems were identified. Of those stars observed for this survey, HD 106506 is the most outstanding target for mapping active regions. It is an apparently young and single star with rapid rotation (v sin i ∼ 80 km s−1), strong Hα chromospheric activity (log R′Hα ∼ −4.2), and deformation of the spectral line profiles indicating the presence of large starspots.

Differential Rotation of the Active G5 V Star κ1 Ceti: Photometry from the MOST Satellite11Based on data obtained with the MOST satellite, a Canadian Space Agency mission jointly operated by Dynacon, Inc., the University of Toronto Institute of Aerospace Studies, and the University of British Columbia.

ABSTRACTAbout 30.5 days of nearly uninterrupted broadband photometry of the solar‐type star κ1 Ceti, obtained with the MOST (Microvariability and Oscillations of Stars) satellite, shows evidence for two large starspots with different rotation periods of 8.9 and ∼9.3 days (ΔΩ/Ω≃4%). Ground‐based measurements of Ca ii H and K emission in 2002 and 2003 reveal variations in chromospheric activity with a period of about 9.3 days. The data were obtained during the MOST commissioning phase. When the data are combined with historical observations, they indicate that the 9.3 day spot has been stable in its period for over 30 yr. The photometry, with a sampling rate of approximately once per minute, was also used to search for acoustic (p‐mode) oscillations in the star. We detect no clear evidence for p‐modes in the κ1 Ceti photometry, with a noise level around 7–9 μmag at frequencies in the range of 0.5–4 mHz (3 σ detection limit of 21–27 μmag). There were no flares or planetary transits during 30.5 days of MOST monitoring with light amplitudes greater than 2 mmag (durations >200 minutes) and 3 mmag (2–200 minute durations). While this rules out any close‐in planets with Jupiter diameters ≥0.5 and orbital inclinations close to 90°, the scatter in differential radial velocities permit a close giant planet in a more highly inclined orbit.

UV piscium and the radiative flux scale

Studies of eclipsing binaries with Hipparcos parallaxes are found to define a radiative flux relation for main sequence stars in the spectral range from B6 – F0which is about as well as to the stars derived from angular diameters. At lower temperatures the fluxes of the components fall below this curve which is caused due to the large intrinsic variations and starspots. From the present analysis it is found that the secondary component of UV Piscium, a late type eclipsing binary, is a normal K3V star and it fits the radiative flux-colour relation quite satisfactorily. This is explained due to the reliable values of the fluxes and colours derived from the clean light curves (light curves obtained after removing the effect of the distortion wave). However, the primary component which is also responsible for the intrinsic variations and starspots continue to deviate from this curve.

1982-1988 Photometry of the Totally Eclipsing Chromospherically Active Binary V792 Herculis=HD 155638

view Abstract Citations (6) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS 1982-1988 Photometry of the Totally Eclipsing Chromospherically Active Binary V792 Herculis=HD 155638 Kaye, A. B. ; Hall, D. S. ; Patterson, L. R. ; Nations, H. D. ; Heckert, P. A. ; Summers, D. L. Abstract We present 1985-1988 UBV and VRI photometry obtained at three different observatories and analyze it along with previously published 1982-1984 UBV photometry. New times of midprimary eclipse along with previously published times yield the improved orbital ephemeris T(pri.min.)=JD 2446674.185 (±0.007) +27d53707(±0d.00026)n. Periodogram analysis of previously published radial velocities, for both the K giant and the F subgiant, yields orbital ephemeris constants consistent with the one above, but of lesser precision. Fitting the seven years of photometry with a cos(2θ) curve, after removing the eclipse points, yields 0m.021±0m.006 for the full amplitude of the ellipticity effect in V. Residuals from that cos(2θ) fit give light curves which reveal continuing starspot variability, which had been seen in the 1982-1984 photometry. These residuals, in ten data groups, are analyzed with a two-spot light-curve fitting procedure. Six long-lived spots are identified, the largest producing a light loss of 0m.166 in V. Lifetimes were >2.85, 0.81, 1.88, 1.84, >0.58, and >0.45 yr. Rotation periods for these six spots have a mean of 27d.36±0d.06, thus confirming synchronous rotation, and a range which indicates a differential rotation coefficient of k=0.031. With respect to the value of 0.65 below which strong dynamo action is expected in a convective star, the Rossby number for the K giant, believed to be the spotted star, is 0.17, well below the threshold and so large starspots are expected. Publication: The Astronomical Journal Pub Date: March 1996 DOI: 10.1086/117877 Bibcode: 1996AJ....111.1322K Keywords: STARS: INDIVIDUAL: HD 155638; BINARIES: ECLIPSING full text sources ADS | data products SIMBAD (1)

Solar and stellar magnetic flux tubes

The magnetic field of the Sun is mainly concentrated into intense magnetic flux tubes having field strengths of the order of 1 kG. In this paper an overview is given of the thermal and magnetic properties of these flux tubes, which are known to exhibit a large range in size, from the smallest magnetic elements to sunspots. Differences and similarities between the largest and smallest features are stressed. Some thoughts are also presented on how the properties of magnetic flux tubes are expected to scale from the solar case to that of solar-like stars. For example, it is pointed out that on giants and supergiants turbulent pressure may dominate over gas pressure as the main confining agent of the magnetic field. Arguments are also presented in favour of a highly complex magnetic geometry on very active stars. Thus the very large starspots seen in Doppler images probably are conglomerates of smaller (but possibly still sizable) spots.

Starspots found on the ellipsoidal variable V350 lacertae = HR 8575

It has been a puzzle why this chromospherically active, strong-dynamo K2 IV-III star is not known to have the large starspots characteristic of other such stars. Published individual radial velocities, which had never been analyzed, are used to derive an orbital solution. Combined with the one older existing orbital solution, this yields an improved orbital ephemeris: time of conjunction (K star behind) = JD 2445255.47 +/- 0.11 days and period = 17.75346 +/- 0.00016 days. All available photoelectric photometry, from 1970.9 to 1992.5, is collected A cos 2 theta fit of the ellipticity effect yields JD 2445255.60 +/- 0.06 days for a time of conjunction, 17.7523 +/- 0.0005 days for the period, and 0.084 mins for the peak-to-peak amplitude in V. With the ellipticity effect removed, the light curve does show measurable starspot variability in 15 of 16 data groups, the starspot wave amplitudes ranging between 0.03 mins and 0.08 mins. Ten starspots are identified and their rotation periods determined, the mean being 17.70 +/- 0.03 days (confirming synchronous rotation) and the range being Delta P/P = 0.017 +/- 0.006 (indicating differential rotation). There is a slow variation in mean brightness, almost 0.1 min in range and at least 2 decades in length.

Directivity of the radio emission from the K1 dwarf star AB Doradus

We present measurements of the spectrum and polarization of the flaring radio emission from the K1 dwarf star AB Doradus, together with previously reported single frequency measurements (with no polarization information) on 3 other days. On all 4 days spanning a 6 month period, the emission was strong and, when folded with the stellar rotation period, showed similar time variations with two prominant peaks at phase 0.35 and 0.75. These peaks coincide in longitude with two large starspots identified from the stellar optical light curve and have half-powe widths as small as 0.1 rotations and no larger than 0.2 rotations. The modulated emission shows no measurable circular polarization, and its two peaks have different turnover frequencies.

First conclusive evidence for rotational modulation of stellar radio emission

We present what we believe to be the first conclusive evidence for rotational modulation of stellar radio emission, observed on the young and rapidly rotating K1 dwarf star AB Doradus (HD 36705). The radio emission of this star peaked near two stellar longitudes where large starspots have been observed to form preferentially. One of the peaks in radio emission was coincident with the central meridian passage of a large starspot; the starspot associated with the other peak may have been overwhelmed by the visible starspot

Long-term starspot activity of short-period RS Canum Venaticorum stars. II - RT Andromedae

view Abstract Citations (56) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Long-Term Starspot Activity of Short-Period RS Canum Venaticorum Stars. II. RT Andromedae Zeilik, M. ; Cox, D. A. ; de Blasi, C. ; Rhodes, M. ; Budding, E. Abstract The photometric distortion waves in the light curves of the short-period RS CVn system RT And are parameterized by means of a dark, circular starspot model. The light curves are drawn from archival sources and 1987 and 1989 observations. The longitudes, latitudes, and areas of the active regions are inferred and the information content of the archival data is evaluated. It is concluded that one large starspot region on the primary star at high latitude and near quadrature longitudes can account for the major maculation effects since 1920. The temperature difference between the spotted region and the photosphere is 1100 to 1200 K. Good quality light curves result in an eccentricity (e = 0.026) and major axis orientation consistent with those reported by others using different procedures. Publication: The Astrophysical Journal Pub Date: October 1989 DOI: 10.1086/167968 Bibcode: 1989ApJ...345..991Z Keywords: Andromeda Constellation; Astronomical Photometry; Binary Stars; Light Curve; Starspots; Emission Spectra; Line Spectra; Radio Emission; Stellar Spectra; Astrophysics; STARS: BINARIES; STARS: INDIVIDUAL CONSTELLATION NAME: RT ANDROMEDAE full text sources ADS | data products SIMBAD (1) Related Materials (4) Part 1: 1986BAAS...18..955Z Part 3: 1990ApJ...354..352Z Part 4: 1990ApJ...363..647Z Part 5: 1994ApJ...421..303Z

The RS CVn Type Star PZ Tel

AbstractWe present broadband photoelectric light curves for the RS CVn type star PZ Telescopium for 1980, 1982 and 1983. The photometric period is about 0.943 days. The V light curve shows radical changes in form and range over a few months, and may be continuously variable. B and V data were obtained in 1982 and 1983. In 1982 no (B-V) change with phase was detected. However, in the first part of the 1983 observing season, a (BV) change of around 0.02 magnitude was found. Also at this time, maximum light was some 0.05 magnitude above that measured previously. Our preliminary spectroscopic data obtained in 1983 indicate that PZ Tel is a double lined binary whose components are of approximately equal luminosities, but this is yet to be confirmed. We suggest that the photometric variations are due to the presence of large cooler starspots on the photosphere of one or both components, as seems to be the case for related systems. The rapid changes in the observed light curve imply equally rapid changes in the distribution of the starspots, and make this an interesting object for further study.

DOPPLER IMAGING OF SPOTTED STARS : APPLICATION TO THE RS CANUM VENATICORUM STAR HR 1099.

ABSTRACT A technique for imaging the surfaces of certain rapidly rotating spotted stars is discussed. The method exploits the correspondence between wavelength position across a rotationally broadened spectral line and spatial position across the stellar disk. Preliminary Doppler Images of the RS CVn star HR 1099 show spots which exhibit a striking similarity in shape and location to X ray images of solar coronal holes. It is suggested that the large star spots on RS CVn's and other active late-type stars emerge at low latitude as scaled-up analogs of solar complexes, but as they migrate poleward, they more closely resemble photospheric analogs of solar coronal holes. The evolution of starspots appears remarkably similar to that of large-scale magnetic fields of the sun.

Periodic light variations in four pre-main-sequence K stars

view Abstract Citations (146) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Periodic light variations in four pre-main-sequence K stars. Rydgren, A. E. ; Vrba, F. J. Abstract Four pre-main-sequence K stars with weak line emission (HD 283447, V410 Tau, and two of the X-ray stars studied by Feigelson and Kriss, 1981) have been monitored with UBVRI photometry during seven consecutive nights in 1981 October. All four stars show quasi-sinusoidal light variations, apparently due to the presence of large starspots. The light variations have amplitudes of from 0.06 to 0.23 mag in yellow light and periods ranging from 1.9 to 4.1 days. Several significant UV flares were also observed. The observations indicate that these young stars possess magnetic surface activity similar to that seen in the RS CVn and BY Dra stars. The observed stars fall within rather than below the T Tauri band in the H-R diagram and have deduced rotational velocities comparable to those of typical T Tauri stars. Relatively rapid rotation in a late-type pre-main-sequence star is apparently not a sufficient condition for producing the strong line and continuum emission which characterizes true T Tauri stars. Publication: The Astrophysical Journal Pub Date: April 1983 DOI: 10.1086/160858 Bibcode: 1983ApJ...267..191R Keywords: K Stars; Late Stars; Main Sequence Stars; Stellar Rotation; Stellar Spectrophotometry; Variable Stars; Angular Velocity; Emission Spectra; Light Curve; Line Spectra; Starspots; T Tauri Stars; Ubv Spectra; X Ray Sources; Astrophysics full text sources ADS | data products SIMBAD (12)

A spectroscopic, photometric, and magnetic study of the starspot on II Pegasi

A description is presented of extensive observations of II Peg during 1977 and 1978, taking into account multicolor broad-band photometry, high-dispersion spectroscopy, low-dispersion spectrophotometry, and Zeeman analysis. During this time the star showed periodic light variations in excess of a 0.4 mag range attributable to the presence of a large starspot or an equivalent nonuniform surface brightness distribution. The high-precision multicolor photometry, which differed greatly from previous photometric results, illustrates that the starspots on II Peg are continually evolving on time scales of approximately 1 year or less. A low-dispersion spectrum of the large spot showed pronounced VO and TiO molecular adsorption features. A high-resolution, high signal-to-noise Reticon spectrum at lambda 6707 does not show any compelling evidence of previously reported lithium in this star.

Is the Close Binary XY Ursae Majoris a Radio Star?

AbstractThe optical position of the short period eclipsing binary XY UMa, which shows large scale star spot activities, coincides within 2 minutes of arc with a radio source, listed in the 4C-, 4CP-, OK-catalogues, and the position obtained with the Effelsberg radio telescope. A fainter star, centered on the radio source position, is according its U-, B-, V-values a K main sequence star. The radio source is non-thermal, and has a spectral index α ~-0.85. If the radio source is identical with the binary, it would imply important consequences about the extragalactic nature of high latitude 4C-sources, the radio background and the high radio luminosity of the binary.

Possible evidence for the occurrence of magnetic fields of order 10 kilogauss in the red dwarf star by Draconis

Koch and Pfeiffer have reported the presence of linear polarization in broad-band observations of the light from the spotted dwarf BY Dra. Here the hypothesis that the polarization is produced by the cumulative effects of the Zeeman patterns of individual absorption lines within the bandpass is examined. The polarization expected in a cool (theta/sub eff/=1.5) dwarf observed in UBVR filters is computed. Comparing results with observations of BY Dra, it is found that the surface field strength on this star is at times of order 10 kilogauss. Peak linear polarization is observed to occur when the site previously occupied by a large starspot is optimally visible. It is suggested that the presence of fields of order 10 kilogauss in an old bipolar region is consistent with a recent model of starspots on a cool dwarf. (AIP)