Observations Of Variable Stars Research Articles

The orbital period and variability of the dwarf nova ES Draconis

A radial velocity study of the cataclysmic variable ES Dra (PG 1524+622) is presented. ES Dra is found to have an orbital period of 0.17660 ± 0.00006 day (4.2384 ± 0.0014 h). The mass-losing secondary star of ES Dra is detectable in the spectrum, and it has a spectral type of M2 ± 1. From this, we estimate the absolute magnitude of ES Dra during our spectroscopic observations to have been M R = 6.5 ± 0.5, and its distance to be 720 ± 150 pc. The long-term light curve of ES Dra compiled by the American Association of Variable Star Observers (AAVSO) shows that ES Dra is a Z Cam star, which between 1995 and 2009 spent most of its time in standstill.

Stochastic variability of luminous blue variables

Using the archives of the American Association of Variable Stars Observers and our own data, we analyse the long-term variability of several well-studied luminous blue variables (LBVs) aiming on a general picture of stochastic variability of these objects. The power density spectra of all the selected objects may be generally described by a single power law contaminated by observational noise at higher frequencies. The slopes of the power-law component are close to p = 2 (where PDS ∝ f − p , and f is frequency) for strongly variable flaring objects like AG Car and significantly smaller ( p ∼ 1.3) for P Cyg where brightness variation amplitude is ≲ 1 m and dominated by slow low-amplitude variability. The slope holds for about two orders of magnitude in the frequency domain, though peaks and curvatures are present at f ≃ 10 −2–10 −3 d −1. We show that pseudo-photosphere approach to variability may explain the power-law shape of the variability spectrum at higher frequencies. However, the observed spectra are actually rather “red” than “brown”: flux variations are correlated up to tens of years that is much longer than the characteristic refreshment time scales of the pseudo-photosphere. We propose that several stochastic noise components produce the power spectra of LBVs.

‘Bridging the gap’ through Australian cultural astronomy

AbstractFor more than 50,000 years, Indigenous Australians have incorporated celestial events into their oral traditions and used the motions of celestial bodies for navigation, time-keeping, food economics, and social structure. In this paper, we explore the ways in which Aboriginal people made careful observations of the sky, measurements of celestial bodies, and incorporated astronomical events into complex oral traditions by searching for written records of time-keeping using celestial bodies, the use of rising and setting stars as indicators of special events, recorded observations of variable stars, the solar cycle, and lunar phases (including ocean tides and eclipses) in oral tradition, as well as astronomical measurements of the equinox, solstice, and cardinal points.

Photometry of the Cataclysmic Variables V1159 Ori and BZ UMa

V1159 Ori is an ER UMa sub-type cataclysmic variable belonging to the SU UMa type, and the controversial BZ UMa lies between the U Gem type and the WZ Sge type, but it possesses also the periodicity characteristics of SU UMa. We have made photometric observations of these two cataclysmic variables with the 1m RCC optical telescope in Yunnan Astronomical Observatory from Feb. 24th to 25th, 2008. The obtained light curves of V1159 Ori exhibit superhumps in the descending stage of a normal outburst, this provides an observational evidence for the universal existence of superhumps in ER UMa-type stars. During our observations BZ UMa was at the maximum of an outburst, but no evident superhump period was detected. The previous observations made by AAVSO (American Association of Variable Star Observers) also have never found any definite superhump. This demonstrates that BZ UMa probably is not a SU UMa-type variable. According to the range of its magnitude variations, BZ UMa is closer to WZ Sge.

LONG-TERM LIGHT CURVE OF HIGHLY VARIABLE PROTOSTELLAR STAR GM CEP

We present data from the archival plates at Harvard College Observatory and Sonneberg Observatory showing the field of the solar type pre-main sequence star GM Cep. A total of 186 magnitudes of GM Cep have been measured on these archival plates, with 176 in blue sensitivity, 6 in visible, and 4 in red. We combine our data with data from the literature and from the American Association of Variable Star Observers to depict the long-term light curves of GM Cep in both B and V wavelengths. The light curves span from 1895 until now, with two densely sampled regions (1935 to 1945 in B band, and 2006 until now in V band). The long-term light curves do not show any fast rise behavior as predicted by an accretion mechanism. Both the light curves and the magnitude histograms confirm the conclusion that the light curves are dominated by dips (possibly from extinction) superposed on some quiescence state, instead of outbursts caused by accretion flares.Our result excludes the possibility of GM Cep being a FUor, EXor, or McNeil's Nebula type star. Several special cases of T Tauri stars were checked, but none of these light curves are compatible with that of GM Cep. The lack of periodicity in the light curve excludes the possibility of GM Cep being a KH 15D system.

The Astronomy Education Research Charter

The Astronomy Education Research Charter is a statement from members of the astronomy education research community. It was originally discussed at the 2007 Astronomy Education Research Symposium. A report of the symposium and a call for public participation in its creation was published in this journal (Price et al. 2008, Astronomy Education Review, 6, 130). Participants of the symposium and members of the general public edited this document via an anonymous wiki from January, 2008 to September, 2008. This published version of the document is authored by all contributors to the wiki, who are represented by the coordinator, Aaron Price, and the coordinating organizations: The American Association of Variable Star Observers and the Wright Center for Science Education at Tufts University. We consider this an ongoing process, and this is just the first version of this document, which is owned by the community. Further revisions are encouraged via the wiki at (uri: http://aavso.org/astroed/index.php/MaiṉPage). The community is welcome to build on this version through other channels as well. In those cases, the wiki may be a useful resource to publicize further work on the charter.

Discovery of an Unusual High State in the Long-Term Light Curve of AM Herculis

ABSTRACTThe magnetic cataclysmic variable archetype AM Herculis is known to display high and low photometric states, in which it switches from Roche lobe-overflow accretion (high) to wind accretion (low). The origin of this behavior is still unknown (although it is believed to be linked to the presence of starspots located near the L1 point on the secondary star), as are the specifics of duration and frequency of the two states. During the recent (2007) transition from an exceptionally long period of persistent low state behavior back to the high state, AM Her entered a short (∼2 month) intermediate state, in which its brightness remained at ∼0.5 mag fainter than the normal high-state level. Within the recorded history of AM Her, this was the first time the system displayed such behavior. Using data from the American Association of Variable Star Observers, we compare the characteristics of this faint high state to the subsequent normal high state, and a prior “failed high state,” in which the system briefly reached a brightness level near that of the normal high state before rapidly returning to the low state. The distribution of magnitude values attained during each state, along with the shapes of the orbital light curve in each state, support a scenario in which the specific configuration of the accretion flow between the secondary star and the white dwarf must be rapidly established at the end of a low state, even before the mass transfer rate has reached the normal high-state level.

Wide-field plate archives stored in the Ukrainian observatories

The latest version of the Wide-Field Plate Database Catalogue of Wide-Field Plate Archives (April 2008) contains 43 archives stored at some Ukrainian observatories, namely, at the Main Astronomical Observatory of the National Academy of Sciences of Ukraine (Golosiiv, Kyiv), at the Crimean Astrophysical Observatory (Nauchnyi and Simeiz), at the Kyiv, L’viv, and Odesa University Observatories, and at the Mykolaiv Observatory. About 126000 plates were obtained from 1898 to 2005 in the framework of the following observing programmes: Solar System Bodies Observations, Observations of Variable Stars, Investigations of the Emission Nebulae and Connected Stars, Spectral Classification of the Stars and Determination of the Stellar Absorption in the Direction of the Emission Nebulae, Photographic Survey of the Northern Sky (FON), Investigation of the Kinematics and Structure of the Main Meridian Section of our Galaxy (MEGA), Observation of Selected Reference Stars, Artificial Satellites Observations and other. At the moment the basic information on 12609 plates from 13 plate archives of the Main Astronomical Observatory and Crimean Astrophysical Observatory is included into the Wide-Field Plate Database Catalogue of Wide-Field Plate Indexes (Sofia, Bulgaria). The plate digitization is just started with flatbed scanners. Some illustrations of the potential of the Ukrainian plate archives for future reusage are given and some compiled plate catalogues are presented on the basis of data from the Wide-Field Plate Database.

Application of the trend filtering algorithm to the MACHO database

Due to the strong effect of systematics/trends in variable star observations, we employ the Trend Filtering Algorithm (TFA) on a subset of the MACHO database and search for variable stars. TFA has been applied successfully in planetary transit searches, where weak, short-lasting periodic dimmings are sought in the presence of noise and various systematics (due to, e.g., imperfect flat fielding, crowding, etc). These latter effects introduce colored noise in the photometric time series that can lead to a complete miss of the signal. By using a large number of available photometric time series of a given field, TFA utilizes the fact that the same types of systematics appear in several/many time series of the same field. As a result, we fit each target time series by a (least-square-sense) optimum linear combination of templates and frequency-analyze the residuals. Once a signal is found, we reconstruct the signal by employing the full model, including the signal, systematics and noise. We apply TFA on the brightest ~5300 objects from subsets of each of the MACHO Large Magellanic Cloud fields #1 and #79. We find that the Fourier frequency analysis performed on the original data detect some 60% of the objects as trend-dominated. This figure decreases essentially to zero after using TFA. Altogether, We detect 387 variables in the two fields, 183 of which would have remained undetected without using TFA. Where possible, we give preliminary classification of the variables found.

Amateur observations of variable stars: The French Association of Variable Stars Observers

AbstractWe briefly present the history and activities of amateur and professionnal astronomers from the “Association Française des Observateurs d'Etoiles Variables” (AFOEV, the French society of variable star observers).

Pulsation-Driven Winds from High Luminosity Stars

Based on 1-dimensional numerical simulations including the rotational acceleration in a quasi-spherical approximation we present pulsation-driven mass loss from luminous stars. In particular, for our model WN8 with M = 60 M ๏ , L = 8×10 5 L ๏ and T eff = 25 000 K with a rotation rate of v sin i = 160 km s -1 given at the stellar photosphere of R p = 47.6 R ๏ and a stellar pulsation of P = 4.144 days we compute a time-dependent mass loss with an averaged rate of 1.28×10 -4 M ๏ /yr. Further implications of such theoretical models are briefly discussed for observations of variable stars with large amplitudes.

Edward Schenfeld: Visual photometry of variables: I. Comparison stars

Based on the SIMBAD database, we collected necessary information on the comparison stars used by E. Schenfeld in observations of variable stars in the 19th century.

Further Studies of the Photometric Variability of Bright Pulsating Red Giants

ABSTRACTLong-term photoelectric V photometry of 13 pulsating red giants (TV Psc, EG And, RZ Ari, η Gem, V614 Mon, RS Cnc, VY UMa, FS Com, SW Vir, R Lyr, EU Del, V1070 Cyg, and W Cyg) from a robotic telescope (APT) and from the photoelectric photometry program of the American Association of Variable Star Observers has been merged to form data sets that are significantly longer and denser than the subsets, and have been analyzed using Fourier and self-correlation techniques. Improved values of the pulsation periods, and especially of the enigmatic long secondary periods (LSPs), have been determined. Most of the stars also show very slow, small variations in amplitude and mean magnitude on timescales of thousands of days. The amplitude variability has also been studied, using both least-squares and wavelet analysis; the dominant amplitude variability is on a timescale of years. The period of EU Del shows neither long-term secular changes nor random cycle-to-cycle fluctuations. APT VRI photometry for 16 stars has been analyzed: for both the pulsation periods and for the long secondary periods (with one notable exception—EG And), the amplitude decreases with increasing wavelength.

The unusual Nova Cygni 2006 (V2362 Cygni)

Context. Optical nova lightcurves often have structures, such as rapid declines and recoveries, due to nebular or dusty phases of the ejecta. Nova Cygni 2006 (V2362 Cyg) underwent an unusual brightening after an early rapid decline. The shape of the lightcurve can be compared to that of V1493 Aql, but in that case the whole event was not as bright and only lasted a couple of weeks. V2362 Cyg had a moderately fast decline of t2 = 9.0 ± 0.5 days before rebrightening, which lasted 250 days after maximum. Aims. We present an analysis of our own spectroscopic investigations in combination with American Association of Variable Star Observers (AAVSO) photometric data covering the whole rebrightening phase until the return to the final decline. Methods. We used medium resolution spectroscopy obtained in ten observing nights in the course of 79 nights to investigate the change of the velocity structure of the ejecta. The publicly available AAVSO photometry was used to analyze the overall properties and the energy of the brightening. Results. Although the behavior of the main outburst (velocity, outburst magnitude, and decline timescales) resembles a “normal” classical nova, the shell clearly underwent a second fast mass ejecting phase, causing the unusual properties. The integrated flux during this event contributes ≈40% to the total radiation energy of the outburst. The evolution of the Hα profile during the bump event is obtained by subtracting the emission of the detached shells of the main eruption by a simple optically-thin model. A distance of D ≈ 7.5 +3.0 −2.5 kpc and an interstellar extinction E(B − V) = 0. m 6 ± 0. m 1 was also derived.

The structure of the October/November 2005 outburst in OJ287 and the precessing binary black hole model

Aims. The blazar OJ 287 had its biggest optical outburst in over 20 years. It occurred in October/November 2005 and was somewhat expected since similar outbursts had occurred at approximately 12 yr intervals since the early 1900s. However, a strict periodicity would have put the event nearly a year later. Here we ask whether the October/November 2005 outburst was indeed the expected 2006 outburst of OJ287. Did it follow the typical light curve behaviour of such events: a rapid initial rise in just over a week and a slower decay in the following months? Methods. In this study we use the extensive observations of The British Astronomical Association Variable Star Section, complemented by the data from The American Association of Variable Star Observers. We compare the 2005 outburst with the previous season's first peak of 1983. Results. We find that the beginning of the 2005 outburst occurred at 2005.76, a few weeks earlier than was reported previously. The timing of the outburst is consistent with the binary black hole model of Lehto and Valtonen. In accordance with this model, we find that the outburst's structural time scale is slower in 2005 than in 1983, while the 2005 outburst was fainter than the 1983 outburst, making the two outbursts about equal in energy. Thus it is quite reasonable to argue that the 2005 outburst was the expected first of the season in the optical light curve of OJ287.

Variability in red supergiant stars: pulsations, long secondary periods and convection noise

We study the brightness variations of galactic red supergiant stars using long-term visual light curves collected by the American Association of Variable Star Observers (AAVSO) over the last century. The full sample contains 48 red semiregular or irregular variable stars, with a mean time-span of observations of 61 years. We determine periods and period variability from analyses of power density spectra and time-frequency distributions. We find two significant periods in 18 stars. Most of these periods fall into two distinct groups, ranging from a few hundred to a few thousand days. Theoretical models imply fundamental, first and possibly second overtone mode pulsations for the shorter periods. Periods greater than 1000 days form a parallel period-luminosity relation that is similar to the Long Secondary Periods of the Asymptotic Giant Branch stars. A number of individual power spectra shows a single mode resolved into multiple peaks under a Lorentzian envelope, which we interpret as evidence for stochastic oscillations, presumably caused by the interplay of convection and pulsations. We find a strong 1/f noise component in the power spectra that is remarkably similar in almost all stars of the sample. This behaviour fits the picture of irregular photometric variability caused by large convection cells, analogous to the granulation background seen in the Sun.

Spectrophotometric observations of variable stars

We present the results of our visual and near-infrared spectrophotometric observations for 77 variable stars obtained during 1971–1991 in Chile, Armenia, and Bolivia. The quasi-monochromatic, extraatmospheric fluxes from the stars are given in absolute energy units (W m−2 m−1) at all wavelengths of the spectral range at 2.5-nm intervals.

The effect of dust obscuration in RR Telescopii on optical and IR long-term photometry and Fe II emission lines

Aims. Infrared and optical photometric and spectroscopic observations of the symbiotic nova RR Tel are used to study the effects and properties of dust in symbiotic binaries containing a cool Mira component, as well as showing “obscuration events” of increased absorption, which are typical for such Miras. Methods. A set of photometric observations of the symbiotic nova RR Tel in different wavelength bands – visual from 1949 to 2002 and near-infrared (JHKL) from 1975 to 2002 – are presented. The variability due to the normal Mira pulsation was removed from the JHKL data, which were then compared with the American Association of Variable Star Observers’ (AAVSO) visual light curve. The changes of the Fe II emission line fluxes during the 1996-2000 obscuration episode were studied in the optical spectra taken with the Anglo-Australian telescope. Results. We discuss the three periods during which the Mira component was heavily obscured by dust as observed in the different wavelength bands. A change in the correlations of J with other infrared magnitudes was observed with the colour becoming redder after JD 2 446 600. Generally, J−K was comparable, while K −L was larger than typical values for single Miras. A distance estimate of 2.5 kpc, based on the IR data, is given. A larger flux decrease for the permitted than for the forbidden Fe II lines, during the obscuration episode studied, has been found. There is no evidence for other correlations with line properties, in particular with wavelength, which suggests obscuration due to separate optically thick clouds in the outer layers. Conclusions.

The Case for Third Bodies as the Cause of Period Changes in Selected Algol Systems

Many eclipsing binary star systems show long-term variations in their orbital periods, evident in their O - C (observed minus calculated period) diagrams. With data from the Robotic Optical Transient Search Experiment (ROTSE-I) compiled in the SkyDOT database, New Mexico State University 1 m data, and recent American Association of Variable Star Observers (AAVSO) data, we revisit Borkovits and Hegedus's best-case candidates for third-body effects in eclipsing binaries: AB And, TV Cas, XX Cep, and AK Her. We also examine the possibility of a third body orbiting Y Cam. Our new data support their suggestion that a third body is present in all systems except AK Her, as is revealed by the sinusoidal variations of the O - C residuals. Our new data suggest that a third body alone cannot explain the variations seen in the O - C residuals of AK Her. We also provide a table of 143 eclipsing binary systems that have historical AAVSO O - C data with new values computed from the SkyDOT database.

A Recurrence Time versus Orbital Period Relation for the Z Camelopardalis Stars

ABSTRACTWe examine AAVSO (American Association of Variable Star Observers) light curves of 16 Z Camelopardalis systems with measured orbital periods, with particular focus on intervals away from standstill. During these times, most of the systems display a sawtooth‐like outburst behavior, with quiescent intervals comparable to the outburst durations. We report the discovery of a linear relation between the characteristic outburst period and orbital period for these systems, which is given by 〈Pout(days)〉 = 62.0(± 7.7)Porb(days) + 2.41(± 1.87).