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Epsilon Aurigae - Aufruf zur photometischen und spektroskopischen Zusammenarbeit.
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| The Recurrent Eclipse of an Unusual Pre-Main-Sequence Star in IC 348
The recurrence of a previously documented eclipse of a solar-likepre-main-sequence star in the young cluster IC 348 has been observed.The recurrence interval is 4.7+/-0.1 yr, and portions of 4 cycles havenow been seen. The duration of each eclipse is at least 3.5 yr, or ~75%of a cycle, verifying that this is not an eclipse by a stellarcompanion. The light curve is generally symmetric and approximatelyflat-bottomed. Brightness at maximum and minimum have been rather stableover the years, but the light curve is not perfectly repetitive orsmooth, and small variations exist at all phases. We confirm that thestar is redder when fainter. Models are discussed, and it is proposedthat this could be a system similar to KH 15D in NGC 2264. Specifically,it may be an eccentric binary in which a portion of the orbit of onemember is currently occulted during some binary phases by a circumbinarydisk. The star deserves sustained observational attention for what itmay reveal about the circumstellar environment of low-mass stars ofplanet-forming age.
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 180: zeta Aurigae
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| Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| Improved Baade-Wesselink surface brightness relations
Recent, and older accurate, data on (limb-darkened) angular diameters iscompiled for 221 stars, as well as BVRIJK[12][25] magnitudes for thoseobjects, when available. Nine stars (all M-giants or supergiants)showing excess in the [12-25] colour are excluded from the analysis asthis may indicate the presence of dust influencing the optical andnear-infrared colours as well. Based on this large sample,Baade-Wesselink surface brightness (SB) relations are presented fordwarfs, giants, supergiants and dwarfs in the optical and near-infrared.M-giants are found to follow different SB relations from non-M-giants,in particular in V versus V-R. The preferred relation for non-M-giantsis compared to the earlier relation by Fouqué and Gieren (basedon 10 stars) and Nordgren et al. (based on 57 stars). Increasing thesample size does not lead to a lower rms value. It is shown that theresiduals do not correlate with metallicity at a significant level. Thefinally adopted observed angular diameters are compared to thosepredicted by Cohen et al. for 45 stars in common, and there isreasonable overall, and good agreement when θ < 6 mas.Finally, I comment on the common practice in the literature to average,and then fix, the zero-point of the V versus V-K, V versus V-R and Kversus J-K relations, and then rederive the slopes. Such a commonzero-point at zero colour is not expected from model atmospheres for theV-R colour and depends on gravity. Relations derived in this way may bebiased.
| NLTE Radiative Transfer in the Extended Atmospheres and Winds of Cool Stars
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| Angular Diameters of Stars from the Mark III Optical Interferometer
Observations of 85 stars were obtained at wavelengths between 451 and800 nm with the Mark III Stellar Interferometer on Mount Wilson, nearPasadena, California. Angular diameters were determined by fitting auniform-disk model to the visibility amplitude versus projected baselinelength. Half the angular diameters determined at 800 nm have formalerrors smaller than 1%. Limb-darkened angular diameters, effectivetemperatures, and surface brightnesses were determined for these stars,and relationships between these parameters are presented. Scatter inthese relationships is larger than would be expected from themeasurement uncertainties. We argue that this scatter is not due to anunderestimate of the angular diameter errors; whether it is due tophotometric errors or is intrinsic to the relationship is unresolved.The agreement with other observations of the same stars at the samewavelengths is good; the width of the difference distribution iscomparable to that estimated from the error bars, but the wings of thedistribution are larger than Gaussian. Comparison with infraredmeasurements is more problematic; in disagreement with models, coolerstars appear systematically smaller in the near-infrared than expected,warmer stars larger.
| Koordinierte Zusammenarbeit zwischen den VdS-FG 'BAV' und 'Spektroskopie' ?
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| Measuring starspots on magnetically active stars with the VLTI
We present feasibility studies to directly image stellar surfacefeatures, which are caused by magnetic activity, with the Very LargeTelescope Interferometer (VLTI). We concentrate on late typemagnetically active stars, for which the distribution of starspots onthe surface has been inferred from photometric and spectroscopic imaginganalysis. The study of the surface spot evolution during consecutiverotation cycles will allow first direct measurements (apart from theSun) of differential rotation which is the central ingredient ofmagnetic dynamo processes. The VLTI will provide baselines of up to 200m, and two scientific instruments for interferometric studies at near-and mid-infrared wavelengths. Imaging capabilities will be made possibleby closure-phase techniques. We conclude that a realistically modeledcool surface spot can be detected on stars with angular diametersexceeding ~ 2 mas using the VLTI with the first generation instrumentAMBER. The spot parameters can then be derived with reasonable accuracy.We discuss that the lack of knowledge of magnetically active stars ofthe required angular size, especially in the southern hemisphere, is acurrent limitation for VLTI observations of these surface features.
| The ever challenging emission-line binary beta Lyrae
A brief history of investigations of Lyr, an emission-line binary andone of the first ever discovered Be stars is presented. A rather fastprogress in the understanding of this enigmatic object during the pastfifteen years is then discussed in some detail. The current picture ofbeta Lyr is that it is an eclipsing binary in a stage of mass transferbetween the components. The mass-losing star is a B6-8II object, with amass of about 3 M(sun), which is filling the Roche lobe and sendingmaterial towards its more massive companion at a rate of about 2 ×10-5 M(sun) yr-1. This leads to the observed rapidincrease of the orbital period at a rate of 19 s per year. Themass-gaining star is as early B star with a mass of about 13 M(sun). Itis completely hidden inside an opaque accretion disk, jet-likestructures, perpendicular to the orbital plane and a light-scatteringhalo above the poles of the star. The observed radiation of the diskcorresponds to an effective temperature which is much lower than whatwould correspond to an early B star. The disk shields the radiation ofthe central star in the directions along the orbital plane andredistributes it in the directions perpendicular to it. That is why themass-losing star appears brighter of the two in the optical region ofthe spectrum. At present, rather reliable estimates of all basicproperties of the binary and its components are available. However, inspite of great progress in understanding the system in recent years,some disagreement between the existing models and observed phasevariations still variations still remains, both for continuum and linespectrum, which deserves further effort.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/386/492, and from theauthors on CD-Rom.
| Eclipsing Binary Stars: Past, Present, and Future
A brief history of eclipsing binary star light curve analysis and anoverview of the current state of affairs is given. The photometricsearches for extra-solar planets in the next few years will eventuallyresult in millions of light curves and such volumes of data will requirethe efforts of amateur astronomers in their analysis. This article is athinly veiled plea to AAVSO members to join the current efforts of a fewAAVSO members in the observation and analysis of eclipsing binary stars.
| Infrared Photometry of Five Long-Period Binaries
We present and discuss JHKLM photometry for five long-period binaries(VV Cep, ZZ CMi, WY Gem, epsilon Aur, and zeta Aur). The IR radiationfrom WY Gem may contain a component with a period of ~430 days,attributable to temperature pulsations of an M supergiant. The 3.5- and5-micrometer radiation from the eclipsing binary epsilon Aur outside theeclipse exhibits excess (relative to the light from an F supergiant)fluxes which correspond to the emission from a cool source with atemperature of ~1000 K. For the eclipsing binary epsilon Aur, we presentthe hitherto unpublished results of our optical and IR photometry during1982-1985, when a primary eclipse was observed in the system.
| A High-Resolution Survey of Interstellar K I Absorption
We present high-resolution (FWHM ~0.4-1.8 km s-1) spectra,obtained with the AAT UHRF, the McDonald Observatory 2.7 m coudéspectrograph, and/or the KPNO coudé feed, of interstellar K Iabsorption toward 54 Galactic stars. These new K I spectra revealcomplex structure and narrow, closely blended components in many linesof sight. Multicomponent fits to the line profiles yield estimates forthe column densities, line widths, and velocities for 319 individualinterstellar cloud components. The median component width (FWHM) and thetrue median separation between adjacent components are both <~1.2 kms-1. The median and maximum individual component K I columndensities, about 4×1010 and 1012cm-2, correspond to individual component hydrogen columndensities of about 2×1020 and 1021cm-2 and E(B-V)~0.03 and 0.17, respectively. If T istypically ~100 K, then at least half the individual components havesubsonic internal turbulent velocities. We also reexamine therelationships between the column densities of K I, Na I, C I, Li I,Htot, H2, and CH. The four trace neutral speciesexhibit essentially linear relationships with each other over wideranges in overall column density. If C is uniformly depleted by 0.4 dex,then Li, Na, and K are each typically depleted by 0.6-0.7 dex. The totalline of sight values for N(K I) and N(Na I) show roughly quadraticdependences on N(Htot), but the relationships for theensemble of individual clouds could be significantly steeper. Thesequadratic (or steeper) dependences appear to rule out significantcontributions to the ionization from cosmic rays, X-rays, and/or chargeexchange with C II in most cases. Charge exchange with negativelycharged large molecules may often be more important than radiativerecombination in neutralizing most singly ionized atomic species in coolH I clouds, however-suggesting that the true ne,nH, and thermal pressures may be significantly smaller thanthe values estimated by considering only radiative recombination. BothN(CH) and N(H2) are nearly linearly proportional to N(K I)and N(Na I) [except for 1015cm-2<~N(H2)<~1019cm-2, over which H2 makes the transition to theself-shielded regime]. Those relationships appear also to hold for manyindividual components and component groups, suggesting thathigh-resolution spectra of K I and Na I can be very useful forinterpreting lower resolution molecular data. The scatter about allthese mean relationships is generally small (<~0.1-0.2 dex), ifcertain consistently ``discrepant'' sight lines are excluded-suggestingthat both the relative depletions and the relative ionization of Li, C,Na, and K are generally within factors of 2 of their mean values.Differences noted for sight lines in Sco-Oph, in the Pleiades, near theOrion Trapezium, and in the LMC and SMC may be due to differences in thestrength and/or shape of the ambient radiation fields, perhaps amplifiedby the effects of charge transfer with large molecules.
| Large Circumbinary Dust Grains around Evolved Giants?
We have detected continuum emission at 450 μm, 850 μm, and 1.35 mmfrom SS Lep (or 17 Lep), 3 Pup, and probably BM Gem, respectively, whichare likely or confirmed binary systems consisting of at least oneevolved giant. The observed submillimeter fluxes are probably emitted bygrains rather than ionized gas. The fluxes are larger than thoseexpected from a ``normal'' dusty wind; the dust temperature is <=70 Kwithin 6" of the stars. To explain why grains are so cold near the star,we suggest that the emission at λ>=450 μm is produced byparticles as large as 0.1 mm in radius and that these large particlesprobably have grown by coagulation in circumbinary orbiting disks withmasses >=5×1028 g.
| On the rotation period of Capella
We present differential Hα and Hβ photometry of the verybright RS CVn-binary Alpha Aurigae (Capella) obtained with the Viennaautomatic photoelectric telescope in the years 1996 through 2000.Low-level photometric variations of up to 0m.04 are detected inHα. A multifrequency analysis suggests two real periods of 106 +/-3 days and 8.64 +/- 0.09 days, that we interpret to be the rotationperiods of the cool and the hot component of the Capella binary,respectively. These periods confirm that the hotter component of Capellarotates asynchronously, while the cooler component appears to besynchronized with the binary motion. The combined Hα data possiblycontains an additional period of 80.4 days that we, however, believe iseither spurious and was introduced due to seasonal amplitude variationsor stems from a time-variable circumbinary mass flow. The rotationalperiods result in stellar radii of 14.3 +/- 4.6 Rsun and 8.5 +/- 0.5Rsun for the cool and hot component, respectively, and are in goodagreement with previously published radii based on radiometric andinterferometric techniques. The long-period eclipsing binary Aurigaeserved as our check star, and we detected complex light variationsoutside of eclipse of up to 0m.15 in Hα and 0m.20 in Hβ. Ourfrequency analysis suggests the existence of at least three significantperiods of 132, 89, and 73 days. One of our comparison stars (HD 33167,F5V) was discovered to be a very-low amplitude variable with a period of2.6360 +/- 0.0055 days.
| Comparison of Stellar Angular Diameters from the NPOI, the Mark III Optical Interferometer, and the Infrared Flux Method
The Navy Prototype Optical Interferometer (NPOI) has been used tomeasure the angular diameters of 41 late-type giant and supergiant starspreviously observed with the Mark III optical interferometer. Sixteen ofthese stars have published angular diameters based on model atmospheres(infrared flux method, IRFM). Comparison of these angular diametersshows that there are no systematic offsets between any pair of datasets. Furthermore, the reported uncertainties in the angular diametersmeasured using both interferometers are consistent with the distributionof the differences in the diameters. The distribution of diameterdifferences between the interferometric and model atmosphere angulardiameters are consistent with uncertainties in the IRFM diameters of1.4%. Although large differences in angular diameter measurements areseen for three stars, the data are insufficient to determine whetherthese differences are due to problems with the observations or are dueto temporal changes in the stellar diameters themselves.
| New physical elements of HR 7428 and its Hα behaviour.
HR 7428 is a spectroscopic binary composed of a K2II-III and a main-sequence A2 star. Thanks to a new set of radialvelocity measurements from our and IUE spectroscopy we have improved theorbital period determination and the spectroscopic elements of bothcomponents. Combining optical photometry and UV low dispersion IUEspectra we have determined new stellar parameters through photosphericsynthetic spectra using the NextGen models by Hauschildt et al.(\cite{Hau99a}, \cite{Hau99b}). The hot secondary component parametersagree with those of a typical A2 V star while the radius of the primarycool star turns out to be 40 Rsun, i.e. significantly smallerthan a previous estimate of 62 Rsun. The position of the hotand cool component on the H-R diagram is consistent with a normalevolution, without any mass exchange, of this binary system, whose ageis in the range 100-200 Myrs. The system displays a filled-in Hαprofile with significant variations both in depth and width along theorbital phase. In addition to the Hα chromospheric emissioncomponent, we have detected, at some phases, a broad extra-absorptionand emission that we relate to an inter-system cloud. Based onobservations collected at the Catania Astrophysical Observatory, Italy.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| Helium and Carbon Abundances in Late-B and Early-A Supergiants
The abundances of carbon and helium were determined for representativelate-B and early-A supergiants based on the C I lines (9078, 9089, 9095,9112) in the near-IR, C II lines (4267, 6151), and the He I 6678 line,in an aim to investigate the nature of the envelope-mixing in theseevolved stars based on the anomaly (if any) of these elements combinedwith that of N and O published before. It turned out that N tends toincrease with a decrease in C, showing a tendency of conserving the sumof C+N nuclei, which suggests that the anomaly of C and N may bereasonably interpreted as being due to mixing of the CN-processedmaterial. However, this increase/decrease in N/C, indicative ofdredge-up of the H-burning product, is not accompanied by anyHe-enrichment. Even surprisingly, the observed tendency is just theopposite, i.e., [He/H] appears to decrease progressively in accordancewith a lowering of [C/H]. Instead of regarding this apparentcharacteristics as being real, we tentatively speculate that someactivity-related line-weakening mechanism (e.g., irradiance of X-rays)might act on the formation of He I lines, the extent of which isindirectly related to the efficiency of envelope mixing via stellarrotation.
| Infrared Photometry for Variable Stars of Selected Types in 1978-1999
We present and discuss IR observations for 35 stars of differentvariability types averaged over many years. These include about twentysymbiotic stars, four W Ser stars and one Algol, six Miras, etc.
| Intereclipse Spectroscopic Snapshot of epsilon Aurigae with the Hubble Space Telescope
A single-epoch low-resolution Goddard High Resolution Spectrographspectrum of the eclipsing binary epsilon Aurigae was obtained while thesecondary was orbiting toward eclipse by the primary. The spectrum asrecorded between 1175 and 1461 Å is rich with emission andabsorption lines which include stellar and interstellar components. Theemission-line profiles have the appearance of double-peaked emissionwith a stronger red component at a radial velocity of +108 km s^-1, anoverlying unresolved absorption component at -20 km s^-1, and a weakerblue emission bump at ~-92 km s^-1. We compare these observationalresults with known orbital properties of the epsilon Aur binary systemand propose that the emission originates at the inner radius of the disksurrounding the enigmatic secondary. We interpret the kinematic data asa possible means to uncover the underlying stellar masses, and wespeculate about the binary's relationship to other ``high-mass'' models.
| An analysis of Almagest magnitudes for the study of stellar evolution.
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| Is the eclipsing variable EE CEP a cousin of epsilon Aur?
We report the first five-colour Johnson UBVRI observations of the lasteclipse of the long-period (5.7 yr) eclipsing binary EE Cep. We proposethat the star is a member of the Cep OB1 association at a distance of2.75 kpc. Using this assumption, we find that the primary is a B5 brightgiant of radius ~ 10 R_solar and luminosity M_v ~ -3.1. The observationsshow that the obscuring body is not a star-like object. We suggest thatthe invisible companion in EE Cep is a dark, thick disc around alow-luminosity central star or binary, and that the system has a fewimportant similarities to the epsilon Aur system.
| From OAO2 to HST. A quarter of a century of ultraviolet astronomy.
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| Emerging trends of optical interferometry in astronomy
The current status of the high spatial resolution imaging interferometryin optical astronomy is reviewed in the light of theoreticalexplanation, as well as of experimental constraints that exist in thepresent day technology. The basic mathematical interlude pertinent tothe interferometric technique and its applications in astronomicalobservations are presented in detail. An elaborate account of the randomrefractive index fluctuations of the atmosphere producing randomaberrations in the telescope pupil, elucidating the trade offs betweenlong-exposure and short-exposure imaging is given. Further, the othermethods viz., (i) speckle spectroscopy, (ii) speckle polarimetry, (iii)phase closure, (iv) aperture synthesis, (v) pupil plane interferometry,(vi) differential speckle interferometry etc., using single moderate orlarge telescopes are described as well. The salient features of variousdetectors that are used for recording short-exposure images aresummarized. The mathematical intricacies of the data processingtechniques for both Fourier modulus and Fourier phase are analyzed; thevarious schemes of image restoration techniques are examined as wellwith emphasis set on their comparisons. The recent technologicalinnovation to compensate the deleterious effects of the atmosphere onthe telescope image in real-time is enumerated. The experimentaldescriptions of several working long baseline interferometers in thevisible band are summarized. The astrophysical results obtained tilldate are highlighted.
| Starspot photometry with robotic telescopes. UBV(RI)_C and by light curves of 47 active stars in 1996/97
We present continuous multicolor photometry for 47 stars from October1996 through June 1997. Altogether, 7073 V(RI)_c, UBV, and by datapoints, each the average of three individual readings, were acquiredwith three automatic photoelectric telescopes (APTs) at FairbornObservatory in southern Arizona. Most of our targets arechromospherically active single and binary stars of spectral type G to Kbut there are also four pre-main-sequence objects and three pulsatingstars in our sample. The light variability is generally due torotational modulation of an asymmetrically spotted stellar surface andtherefore precise rotational periods and their seasonal variations aredetermined from Fourier analysis. We also report on photometricvariations of gamma CrB (A0V) with a period of 0.44534 days. All dataare available in numerical form. All data are available from CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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