Accuracy in variable star work: The three-star single-channel technique

CoLiTecVS software for the automated reduction of photometric observations in CCD-frames

view Abstract Citations (30) References (6) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometry of the radio variable HR 1099. Bopp, B. W. ; Espenak, F. ; Hall, D. S. ; Landis, H. J. ; Lovell, L. P. ; Reucroft, S. Abstract We present photoelectric observations of the RS CVn -type binary star HR 1099 obtained at four observatories between February 1975 and March 1976 using 10 Tau as a comparison star. There were 101 observations in the V and 12 in the B and R. These data are best satisfied with a period of P , = + 0d 5 Consideration of other RS CVn -type binaries suggests that it should be shorter than the orbital period, orb = 2d.83782 + 0d.00022, by 0d.00054)d.008, but our P,, determination is too imprecise to show this. The 1963 prediscovery observations of Cousins show the same light curve shape and amplitude but the 1 3-yr gap is so long that we cannot use them to refine P,,. Publication: The Astronomical Journal Pub Date: January 1977 DOI: 10.1086/112007 Bibcode: 1977AJ.....82...47B Keywords: Astronomical Photometry; Binary Stars; Light Curve; Radio Sources (Astronomy); Variable Stars; Ephemerides; Orbital Elements; Phase Shift; Sine Waves; Stellar Luminosity; Stellar Magnitude; Ubv Spectra; Astronomy full text sources ADS | data products SIMBAD (2)

In this article, we present the study for the reclassification of the variability of the star CzeV961 by SSV-UAI-GRAV, classified by Variable Star Index as an EW eclipsing binary. In the same field of observation, there were two variable stars already discovered by Gaia but of an undefined type. In examining the comparison stars for our study, we then discovered a new variable star that had not yet been classified. The star CzeV961 turned out to be a Gamma Doradus variable star, like the two Gaia stars, while the newly discovered variable turned out to be an RS Canum Venaticorum type star.

Drift correction for pattern classification with neural networks

In order to detect variable stars in the well known star forming region, the Orion Nebula Cluster, a series of 22 exposures taken from November 1996 to October 1998, using the ESO 100/152cm Schmidt telescope, covering a field of 5° × 5° was analyzed. The films (Kodak Tech-Pan 4415 emulsions, effective spectral range from ~630 nm to 690 nm) were digitized by the SuperCOSMOS machine, the measurements calibrated to the R magnitude of the USNO B1.0 catalogue and differential photometry was performed throughout the whole field. In the process, a set of 260 stars that remained constant in the 22 films and were well distributed over the field was selected and used as comparison stars for the differential photometry of all the other stars in the field. Diverse statistical studies were performed in order to characterize the type and degree of variability of the objects. The 22 films, all exposed for 30 minutes each, were stacked together at our request by the SuperCOSMOS team, producing perhaps the deepest wide field image of M42 ever taken.This database (>150 000 objects, mostly stars and ~2% galaxies) is going to be used as a starting point for the Variable Young Stellar Object Survey (VYSOS) project, which consists of 2 fully automated robotic telescopes of 41cm each, one installed on Mauna Loa (Hawaii, USA) and the other at Cerro Armazones (Chile), both using the Pan STARRS set of photometric filters. We discovered thousands of new variable stars within the 5° × 5° region studied. We have variability statistics for all objects and are classifying the variable stars according to the variability type and amplitude. We intend to make this database available via the WEB.

Variable stars have historically served as tools and laboratories in our understanding of stellar formation and evolution, the formation of star clusters, the calibration of distance determination methods, and a variety of other areas. In particular, the study of eclipsing binaries (EBs) in globular clusters (GCs) can provide direct distance estimates to clusters as well as constraints for the turnoff masses of GC stars. Knowing precise distances to GCs would constitute an independent check of widely used distance determination methods in astronomy. Obtaining masses of GC turnoff stars provides a fundamental test of low-metallicity stellar models that calculate ages for these stars—and thus the GCs themselves—and thereby allow a lower limit estimate of the age of the universe. My dissertation research with M. Mateo at the University of Michigan consists of a monitoring survey of 10 Galactic GCs with the aim of identifying photometrically variable EBs around or below the main-sequence turnoff (MSTO). My thesis work comprises the results of our research on the GCs NGC 3201, M10, and M12. Our observing strategy is aimed at detecting variables with periods between 0.2 and around 5 days and , thereby optimizing our chance to find the 16.5 ! V ! 20 valuable detached EBs in the target clusters. In addition, we correct for differential reddening variations across the cluster fields of up to several tenths of magnitudes in V by internally creating a differential extinction map with an arcminute resolution from our cluster photometry data and calculate the additional reddening zero point using isochrone fitting. The resulting improvement in the appearance of the color-magnitude diagrams (CMDs) of the clusters is considerable (see K. von Braun & M. Mateo 2001, AJ, 121, 1522). We obtained approximately 200 VI epochs with about 20,000 stars per image for each of the three clusters. Analysis of these data revealed the existence of 14 variable stars (11 EBs) in the field of NGC 3201, three variables (one EB) in the field of M10, and two EBs in the field of M12. Spectroscopic followup work showed that only one variable (a blue straggler W Ursa Majoris contact EB) in the field of NGC 3201 is associated with the cluster. Another W UMa EB is most likely a member of M12, based on its location in M12’s CMD and its empirically calculated absolute magnitude. The rest of the variable stars we detected are members of the Galactic disk (see K. von Braun & M. Mateo 2002, AJ, 123, 279; and K. von Braun et al. 2002, AJ, 124, 2067 for details). We thus calculate a ratio of observable, short-period, main-sequence binaries to main-sequence stars of around 1/500 for the Galactic disk (consistent with literature estimates) and 1/9000 for GC members. The latter value is considerably smaller than the commonly quoted value of 1/1000. While the discrepancy may be due to small number statistics, we attribute it to the fact that we lose about 20% of our fields to crowding toward the cluster center where the binary fraction should be highest after a few cluster relaxation times. In my dissertation, I show the cluster fields and CMDs (before and after dereddening) with the locations of the variable stars and our differential extinction maps, as well as the phased light curves and spectra (wherever applicable) of the variable stars. For additional information or to obtain a copy of the dissertation, please contact me or visit http://www.ciw.edu/vonbraun.

view Abstract Citations (16) References (4) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Photo-Electric Study of ɛ Aurigae Huffer, C. M. Abstract The brightness of the variable star Aurigae, which has a period of 27 years, was measured with the photo-electric photometer at the Washburn Observatory on 98 nights between January, 1928, and May, 1931. There was observed the expected loss of light, similar to an eclipse, beginning in April, 1928, and ending in May, 1930. In addition, irregular short-period fluctuations amount- ing to as much as 0.2 mag. were found. These fluctuations were detected at the begin- ning of the observations and they continued during the minimum and to the end of this series. It was hoped that a period coald be found to represent the maxima or minima of these secondary variations. A submultiple of 336 days seemed most likely, but was found to be unsatisfactory. The average interval between maxima or minima is rough- ly of the order of 100 days. The depths of the minima are also unequal and irregular, as well as non-periodic. A correlation with synchronous variations in the spectrum has yet to be established. During what has been called the constant phase of minimum there was also observed a steady decrease of brightness amounting to about oMo6. The mean brightness at maximum light was found to be approximately the same before and after the minimum. The three comparison stars were found to be constant in light. The probable error of a magnitude of determined on one night is ± o~oo6, which is far less than the irregu- larities of the star's light. The following elements were adopted for the primary minimum: t1 = J.D. 2425725+ 9883d E; loss of light =o~'8i; total duration= 754 days Publication: The Astrophysical Journal Pub Date: July 1932 DOI: 10.1086/143395 Bibcode: 1932ApJ....76....1H full text sources ADS |

We describe the results of visual photometry of 111 variable stars observed by Schoenfeld in the 19th century. The entire body of data contains brightness curves in tabulated form, as well as certain additional useful information: graphs of changes in brightness of variable stars and identification tables of comparison stars and stars suspected of variation in brightness.

Die Serie Communications in Asteroseismology (CoAst) stellt eine international gefragte Plattform für wissenschaftliche Publikationen der neuesten Forschungsergebnisse auf dem Gebiet der Asteroseismologie dar. Forschungsgegenstand der Asteroseismologie sind veränderliche und pulsierende Sterne. Neben den halbjährlich erscheinenden regulären Ausgaben mit Beiträgen aus der laufenden Forschung werden auch Sonderausgaben für Konferenzberichte bzw. Programmhandbücher herausgegeben. Volume 153 beinhaltet eine Vielzahl von Arbeiten mit Ergebnissen aus erdgebundenen und satellitengestüzten Beobachtungen pulsierender Sterne sowie über den Vergleich mit theoretischen Modellen. Erstmals berichtet auch das von der EU eingerichtete Forschungsnetzwerk HELAS - European Helio- and Asteroseismology Network - über neue Instrumente und Strukturen für den Daten- und Wissensaustausch unter Astronomen.

An uvby photometric monitoring of a sample of 19 Ba II stars has been performed since July 1984 at ESO on the Danish and ESO 50 cm telescopes, as part of the “Long Term Program for Variable Stars” (Sterken, 1983). The sample contains southern Ba II stars with variable radial velocities (from McClure, 1983 and Jorissen and Mayor, 1988) as well as Ba II stars already monitored by Landolt (1983). The observations are done differentially, using two comparison giants of the same spectral type located within a few degrees of the Ba II star. The reduction to the standard uvby system is performed using the algorithm described in Manfroid and Heck (1983), taking into account all the measurements performed on the considered telescope since the beginning of the monitoring. With such a reduction procedure, the scatter in the magnitude difference between two comparison stars (of magnitude 5 to 7) can be as low as 0.003-0.004 mag rms.

Exoplanet host star activity, in the form of unocculted starspots or faculae, alters the observed transmission and emission spectra of the exoplanet. This effect can be exacerbated when combining data from different epochs if the stellar photosphere varies between observations due to activity. Here, we present a method to characterize and correct for relative changes due to stellar activity by exploiting multi-epoch ( visits/transits) observations to place them in a consistent reference frame. Using measurements from portions of the planet’s orbit where negligible planet transmission or emission can be assumed, we determine changes to the stellar spectral amplitude. With the analytical methods described here, we predict the impact of stellar variability on transit observations. Supplementing these forecasts with Kepler-measured stellar variabilities for F-, G-, K-, and M-dwarfs, and predicted transit precisions by the James Webb Space Telescope’s (JWST) NIRISS, NIRCam, and MIRI, we conclude that stellar activity does not impact infrared transiting exoplanet observations of most presently known or predicted TESS targets by current or near-future platforms, such as JWST, as activity-induced spectral changes are below the measurement precision.

VARIABLE COMPARISON STARS OF OJ 287 AND ON 325

Over the past 100 years geographers have extensively employed in situ observations of the atmosphere in their research endeavors. Technological improvements in instrumentation, communication, and data storage media have played fundamental roles in the expansion of observational networks and in the improved accuracy and precision of measurements. Yet, technological changes, along with technological limitations, such as instrument drift and failure, have introduced unwanted inhomogeneity into the time series of surface and upper-air observations. An additional constraint is that most, if not all, observational networks for the atmosphere were designed for short-range weather prediction rather than for climate monitoring. This essay reviews, for the non-climatologist, the primary surface and upper-air datasets available for climatological research in the U.S. and for global-scale analyses. Particular focus is placed on the known sources of inhomogeneities in these data series. Geographers need to become more aware of the value of in situ surface and upper-air observations and the current limitations and fragility of these networks.

(abridged) Strongly star-forming galaxies of subsolar metallicities are typical of the high-redshift universe. Here we therefore provide accurate data for two low-z analogs, the well-known low-metallicity emission-line galaxies Haro 11 and ESO 338-IG 004. On the basis of Very Large Telescope/X-shooter spectroscopic observations in the wavelength range 3000-24000\AA, we use standard direct methods to derive physical conditions and element abundances. Furthermore, we use X-shooter data together with Spitzer observations in the mid-infrared range to attempt to find hidden star formation. We derive interstellar oxygen abundances of 12 + log O/H = 8.33+/-0.01, 8.10+/-0.04, and 7.89+/-0.01 in the two HII regions B and C of Haro 11 and in ESO 338-IG 004, respectively. The observed fluxes of the hydrogen lines correspond to the theoretical recombination values after correction for extinction with a single value of the extinction coefficient C(Hbeta) across the entire wavelength range from the near-ultraviolet to the NIR and mid-infrared for each of the studied HII regions. Therefore there are no emission-line regions contributing to the line emission in the NIR range, which are hidden in the optical range. The agreement between the extinction-corrected and CLOUDY-predicted fluxes implies that a HII region model including only stellar photoionisation is able to account for the observed fluxes, in both the optical and NIR ranges. All observed spectral energy distributions (SEDs) can be reproduced quite well across the whole wavelength range by model SEDs except for Haro 11B, where there is a continuum flux excess at wavelengths >1.6mum. It is possible that one or more red supergiant stars are responsible for the NIR flux excess in Haro 11B. We find evidence of a luminous blue variable (LBV) star in Haro 11C.

We present high precision N-band spectroscopy of a subsample of ESO mid infrared (MIR) calibration standard stars. The spectra were taken with the TIMMI2 instrument at the ESO/La Silla observatory. The low resolution spectra (R ≈ 160) were analyzed with an optimal extraction procedure specifically designed for TIMMI2 spectroscopy. The wavelength calibration was done using atmospheric lines. Our analysis package is based on IDL and will be made available to the community. We compare the spectro-photometric flux of the 1d-spectra to the spectral irradiance calibration models by Cohen et al. (1999). This allows us to demonstrate that the derived absolute calibration of the spectra is accurate to better than 5% in most cases. Our subsample of MIR calibration standards presented here shall become the primary calibrators of the VISIR instrument. 1 Observations Here is an overview on the basic parameters of the observations: Telescope: ESO 3.6m at La Silla, Chile Instrument: Thermal Infrared Multimode Instrument 2 (TIMMI2) Date of observation: 3 nights in January 2003 Type of observation: Spectroscopy Wavelength range: 7.56 14.04 μm (N-band) Resolution: 0.02 μm/pixel (λ/∆λ = 160) Slit size: 1. 2× 70 Seeing: 0. 7 1. 5 Airmass: ≈ 1.1 (exception: HD 37160 at 1.4) 2 Sources & Data Reduction The spectra of the eight MIR standard stars listed in Table 1 were reduced and analyzed using IDL routines specifically designed for this purpose (see Siebenmorgen et al. (2004) or this issue for more details). The wavelength calibration was done using the ozone atmospheric feature. An extinction correction method for TIMMI2 spectra is presented by Schutz & Sterzik (this issue) but has not been applied yet. ESO Symposia: High Resolution Infrared Spectroscopy in Astronomy, pp. 96–99, 2005. © Springer-Verlag Berlin Heidelberg 2005 Mid Infrared Spectroscopic Standards 97 Table 1. HD number Spectral type Variable Other Model star? designations spectrum by (1) 29291 G8lll no H 32887 K4lll yes Lep C 37160 G8lll-lV no C 81420 K5lll no C 108903 M3.5V yes γ Crux C 110458 K0lll no C 123139 K0lllb no C 133774 K5lll no C (1) Model spectra taken from Cohen et al. (1999) (C) and P. Hammersely (H) 3 Questions There are two main questions to be answered within the course of this work: 1. How well do the measured spectra correspond to the model N-band spectra by Cohen et al. (1999)? 2. Are the results influenced by the choice of calibration source? 4 Results In the following, the results of two out of the three observation nights are presented separately. Each standard star was calibrated with every appropriate other standard star, i.e. one measured at similar airmass and at the same night. When inspecting Fig. 1, it becomes apparent that HD108903 is the only standard star which shows significant deviations from the model spectrum. It is also the only M-type star of the sample. In general it can be stated that the atmospheric ozone absorption feature could not be eliminated in all spectra during the data reduction. Fig. 2 shows that HD 37160 is the only star showing a significant absorption feature at ≈ 12.5 μm. There are two possible reasons for that: • HD 37160 has a real feature at 12.5 μm. • While HD29291 and all the stars from the previous night were observed at an airmass of 1.1, HD 37160 is the only star observed at an airmass of 1.4. Consequently, it could only be calibrated by stars observed at a lower airmass. Thus, it is very likely that this absorption feature is just the residual of the well-known atmospheric absorption line at 12.55 μm which could not be totally eliminated by the reduction routine. This unwanted effect is due to the different airmasses of the science observation and the calibration measurement. 98 Katrin Kampgen & Ralf Siebenmorgen 8 9 10 11 12 13 wavelength (μm) 50 100 150 200 flu x (J y) HD123139 +20 Jy +50 Jy +80 Jy +100 Jy HD133774 HD81420 HD110458 HD108903 HD32887 8 9 10 11 12 13 wavelength (μm) 0 10 20 30 40 flu x (J y) HD110458 +4 Jy +9 Jy +14 Jy +19 Jy HD133774 HD123139 HD81420 HD108903 HD32887 8 9 10 11 12 13 wavelength (μm) 10 20 30 40