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Preliminary determinations of the masses of the neutron star and mass donor in the high mass X-ray binary system EXO 1722-363
Aims: We intended to measure the radial velocity curve of thesupergiant companion to the eclipsing high mass X-ray binary pulsar EXO1722-363 and hence determine the stellar masses of the components. Methods: We used a set of archival K_s-band infrared spectra of thecounterpart to EXO 1722-363 obtained using ISAAC on the VLT, andcross-correlated them in order to measure the radial velocity of thestar. Results: The resulting radial velocity curve has asemi-amplitude of 24.5 ± 5.0 km s-1. When combinedwith other measured parameters of the system, this yields masses in therange 1.5 ± 0.4 - 1.6 ± 0.4 ~Mȯ for theneutron star and 13.6 ± 1.6 - 15.2 ± 1.9~Mȯ for the B0-1 Ia supergiant companion. These lowerand upper limits were obtained under the assumption that the system isviewed edge-on (i = 90°) for the lower limit and the supergiantfills its Roche lobe (β = 1) for the upper limit respectively. Thesystem inclination is constrained to i>75° and the Rochelobe-filling factor of the supergiant is β>0.9. Additionally wewere able to further constrain our distance determination to be 7.1 ≤d ≤ 7.9 kpc for EXO 1722-363. The X-ray luminosity for this distancerange is 4.7 × 1035 ≤ L_X≤ 9.2 ×1036 erg s-1. Conclusions: EXO 1722-363therefore becomes the seventh of the ten known eclipsing X-ray binarypulsars for which a dynamical neutron star mass solution has beendetermined. Additionally EXO 1722-363 is the first such system to have aneutron star mass measurement made utilising near-infrared spectroscopy.Based on observations carried out at the European Southern Observatoryunder programme ID 077.B-0872(A).
| Spectral classification of the mass donors in the high-mass X-ray binaries EXO 1722-363 and OAO 1657-415
Aims: We report near-infrared (NIR) observations of the mass donors ofthe eclipsing high-mass X-ray binary (HMXB) systems EXO1722-363 and OAO 1657-415 in order toderive their accurate spectral classifications. Methods: ESO/VLTobservations of the targets with the NIR spectrometer ISAAC werecompared with several published NIR spectral atlases of O and Bsupergiants, an identification of each object's spectral characteristicswas made, enabling the refinement of spectral classification of the massdonors. Results: We determined that EXO1722-363 was of spectral type B0-B1Ia, positioned at adistance 8.0-2.0+2.5 kpc with a progenitor mass inthe range 30-40 Mȯ. Luminosity calculations imply thatLX ~ 1035-1037 erg s-1 forthis distance range. We conclude that EXO 1722-363shares many of the properties associated with other X-ray binary B-typesupergiant donors. We found that OAO 1657-415correlates closely with the spectra of a class of transitional objects,the Ofpe/WNL stars, an intermediate evolutionary stage between massive Otype stars leaving the main sequence and evolving into Wolf-Rayets. Dueto the wide range in luminosity displayed by Ofpe/WNL stars,(log(L/Lȯ) ~ 5.3-6.2) distance determinations areproblematic. For OAO 1657-415 we report a distance of4.4 ≤ d ≤ 12 kpc, implying an X-ray luminosity of 1.5 ×1036 ≤ LX ≤ 1037 ergs-1. We have used our new classification of OAO1657-415 to explain the physical processes responsible for itsunique position within the Corbet diagram. Ofpe/WNL stars demonstrate ahigh rate of mass-loss through a dense stellar wind combined with a lowterminal velocity. This combination of wind properties leads to a highaccretion rate and transfer of angular momentum to the neutron star inthis system. We believe this in turn leads to a smaller instantaneousequilibrium spin period with respect to normal OB supergiants.Based on observations carried out at the European Southern Observatoryunder programme ID 081.D-0073(A).
| A catalog of bright calibrator stars for 200-m baseline near-infrared stellar interferometry
We present in this paper a catalog of reference stars suitable forcalibrating infrared interferometric observations. In the K band,visibilities can be calibrated with a precision of 1% on baselines up to200 meters for the whole sky, and up to 300 meters for some part of thesky. This work, extending to longer baselines a previous catalogcompiled by Bordé et al. (2002, A&A, 393, 183), isparticularl y well adapted to hectometric-class interferometers such asthe Very Large Telescope Interferometer (VLTI, Glindemann et al. 2003,Proc. SPIE, 4838, 89) or the CHARA array (ten Brummelaar et al. 2003,Proc. SPIE, 4838, 69) when one is observing well-resolved, high-surfacebrightness objects (K 8). We use the absolute spectro-photometriccalibration method introduced by Cohen et al. (1999, AJ, 117, 1864) toderive the angular diameters of our new set of 948 G8-M0 calibratorstars extracted from the IRAS, 2MASS and MSX catalogs. Angular stellardiameters range from 0.6 mas to 1.8 mas (median is 1.1 mas) with amedian precision of 1.35%. For both the northern and southernhemispheres, the closest calibrator star is always less than 10°away.
| 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
| Simultaneous Observations of Variability at All Atmospheric Levels of V824 Arae (HD 155555)
We conducted a multiwavelength campaign observing V824 Ara (HD 155555,G5 IV+K0 IV-V) continuously throughout one complete orbital cycle (~1.7days) in early May of 1996. At the core of this campaign wereobservations using the GHRS on the Hubble Space Telescope (HST). In all,about 48,000 spectra, many in rapid readout mode, were obtained with theGHRS covering the C IV, Mg II, and Fe XXI wavelength regions at 11-15separate phases. Simultaneous observations were made with the ExtremeUltraviolet Explorer (EUVE). Radio observations (3.5 and 6 cm) wereconducted at the Australian Telescope, while ground-based visualspectroscopic and photometric observations were made at EuropeanSouthern Observatory, Cerro Tololo Inter-American Observatory, theAnglo-Australian Telescope, and South African Astronomical Observatory.Additional ground-based observations were obtained before, during, andafter the campaign. Our primary intent was to obtain a three-dimensionalmodel of the atmosphere extending from the photosphere to the corona.Variability was clearly detected, including several flares observed inthe HST, EUVE, and radio data. We present results from modeling theultraviolet transition region lines using an anisotropic macroturbulencemodel. Previous studies of transition region lines in late-type activestars have used multiple Gaussians to fit the observed line profiles,adding broad components to account for the extended wings observed inseveral active systems, including V711 Tau (HR 1099). This broadcomponent has been interpreted as arising from the continuous presenceof microflaring. We demonstrate that anisotropic macroturbulence modelscan also explain the observed Mg II profiles. Based on observations withthe NASA/ESA Hubble Space Telescope, obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS 5-26555.
| Doppler imaging of stellar surface structure --- XIV. The double-lined pre-main-sequence binary V 824 Arae = HD 155555
Photospheric Doppler images for both stellar components of thedouble-lined pre-main-sequence binary V 824 Ara reveal surfacetemperature inhomogeneities of up to 1800 K on both stars. The spotgeometry on the hotter primary is dominated by an elongated, tilted,equatorial feature but our maps from two spectral regions consistentlyalso show a polar spot cooler by 1700 K. The secondary star has spotsmainly at low and very high latitudes but not a full-sized polar cap. Aflux-tube simulation with appropriate stellar models for V 824 Arasuggests that any polar or high-latitude spot must have formed afterflux-tube emergence. Generally, the low-latitude spots on both stellarcomponents appear to be mostly concentrated on the hemispheres turnedaway from each other while the asymmetry of the polar spot on theprimary points in the direction of the orbital motion. We present newradial velocities and use them to re- evaluate the orbital elements andto derive absolute parameters for both stellar components. The absolutebrightness and mass of the two stars suggest that they are very close tothe main sequence - but not yet on the ZAMS - if an inclination of theorbital plane (and rotational axes) of 52̂ is adopted as suggestedby the Doppler imaging. Since both stars are active, we solve for theinclinations of both stellar components separately and find that thevalues agree to within their uncertainties. Based on observationscollected at the European Southern Observatory
| Long-term monitoring of active stars. VIII. UBV(RI)_(c) photometry collected in February 1992
As a part of an extensive program focusing on the global properties andevolution of active stars, high-precision UBV(RI)_c photometry of 31selected stars, collected at the European Southern Observatory over the14-29 February 1992 interval, is presented. Significant evolution of thelight curves, period variations and evidence for long-term variabilityof the global degree of spottedness are found. Some spectralclassifications are revised and the inferred photometric parallaxes arecompared, whenever possible, with the values measured by the Hipparcossatellite. Flare events were detected for the star HD16157 = CC Eri, EXO 055609-3804.4 TY Coland HD 119285 = V851 Cen. Optical variability wasdiscovered for the Pop II binary HD 89499. Theseobservations contribute to the establishment of a time-extendedphotometric database which can give important clues on topics such asthe stability of spotted areas, differential rotation, solar-like cyclesand the correlation between inhomogeneities at different atmosphericlevels. based on data collected at the European Southern Observatory, LaSilla, Chile.
| Long-term monitoring of active stars. VI. UBV(RI)_c observations collected in Sep.-Oct. 1990
In the framework of an extensive program focusing on the globalproperties and evolution of active stars, high-precision UBV(RI)_cphotometry of 9 selected stars, collected at the European SouthernObservatory over the intervals 7-17 September and 30 September - 10October 1990, is presented. Significant evolution of the light curves,period variations and evidence for long-term variability of the globaldegree of spottedness are found. Some of the spectral classificationsare discussed. These observations contribute to the establishment of atime-extended photometric database which can give important clues ontopics such as the stability of the spotted areas, differentialrotation, solar-like cycles and the correlation between inhomogeneitiesat different atmospheric levels. Based on data collected at the EuropeanSouthern Observatory, La Silla, Chile. Tables and the complete data setare also available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr or via http://cdsweb.u-strasbg.fr/Abstract.html
| Long-term monitoring of active stars. V. UBV(RI)_ c_ photometry collected in Feb.-Mar. 1990.
High-precision UBV(RI)_c_ photometry of 12 selected active stars,collected at the European Southern Observatory (La Silla, Chile) overthe period February - March 1990, is presented. Significant evolution ofthe light curves, period variations and, in most cases, evidence forlong-term variability of the global degree of spottedness are found.Some of the spectral classifications are discussed. This paper is partof a more extensive program focusing on the global properties andevolution of active stars and is aimed at establishing a time-extendedphotometric database which can give important clues on topics such asthe stability of the spotted areas, differential rotation and solar-likecycles.
| Longterm Monitoring of Active Stars - Part Three - UBV Ri/c Photometry of 14 Southern Hemisphere Variables
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102..655C&db_key=AST
| UBVRI Observations of the Chromospherically Active Star HD 155555 (V824 Ara) in 1986 and 1987
Not Available
| UBV(RI)c photometry for CaII emission stars. II - Observations at Mt. John University Observatory and at Mt. Stromlo
UBV(RI)c data are given for 17 stars with strong Ca II H and K emission.Techniques of observation and reduction are described briefly.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Oltár |
| Rektaszcenzió: | 17h22m28.71s |
| Deklináció: | -66°16'08.1" |
| Vizuális fényesség: | 7.417 |
| Távolság: | 473.934 parszek |
| RA sajátmozgás: | -0.7 |
| Dec sajátmozgás: | -9.3 |
| B-T magnitude: | 9.352 |
| V-T magnitude: | 7.577 |
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