Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
The Nainital-Cape Survey. II. Report for pulsation in five chemically peculiar A-type stars and presentation of 140 null results
Aims.We search for photometric variability in chemically peculiar A typestars in the northern hemisphere. Methods: .High-speed photometricobservations of Ap and Am star candidates have been carried out fromARIES (Manora Peak, Nainital) using a three-channel fast photometerattached to the ARIES 104-cm Sampurnanand telescope. Results:.This paper presents three new variables: HD 113878, HD 118660 and HD207561. During the time span of the survey (1999 December to 2004January) pulsations of the δ Sct type were also found for the twoevolved Am stars HD 102480 and HD 98851, as reported in Joshi et al.(2002, 2003). Additionally, we present 140 null results of the surveyfor this time span. Conclusions: .The star HD 113878 pulsates witha period of 2.31 h, which is typical of δ Sct stars. HD 118660exhibits multi-periodic variability with a prominent period of nearly 1h. These periods need to be investigated and make HD 118660 aparticularly interesting target for further observations. For HD 207561,a star classified as Am, a probable pulsation with a period of 6 min wasfound in the light curves obtained on two consecutive nights. Both HD102480 and HD 98851 exhibit unusual alternating high and low amplitudemaxima, with a period ratio of 2:1. The analysis of the null resultsconfirms the photometric quality of the Nainital site.
| Facilities at ARIES for the Nainital-Cape Survey
A collaborative programme searching for mmag pulsations in chemicallypeculiar stars in the northern hemisphere was initiated in 1997 betweenNainital, India, and Cape Town, South Africa. It was therefore named asthe Nainital-Cape Survey programme. The detection limits imposed by theobserving conditions (including atmospheric noise and telescope size) atboth Manora Peak and Devasthal sites are described. The scintillationnoise on the best photometric nights is ≈0 1 to 0.2 mmag for thesesites. Both places allow one to detect few mmag variation in brightstars ( ≤12 mag), and are therefore particularly well-suited forcarrying out the proposed survey work. The main characteristics of thethree-channel photometer developed at ARIES for carrying out theobservations are also presented. This excellent instrument has been usedextensively since 1999 at the f/13 Cassegrain focus of ARIES’ 104cm telescope. In particular, it allowed the survey to result in thediscovery of δ Scuti like pulsations in four Am stars, in onerapidly oscillating Ap star, and in a number of probable variables sofar. The future prospects are then presented, which regard theacquisition of a high speed time series CCD photometer, a project tobuild a 3-metre class telescope at Devasthal, and collaborativeobservations with Indian and foreign astronomical sites.
| The Nainital-Cape Survey: A Search for Variability in Ap and Am Stars
The "Nainital-Cape Survey" program for searching photo-metricvariability in chemically peculiar (CP) stars was initiated in 1997 atARIES, Nainital. We present here the results obtained to date. The Amstars HD98851, HD102480, HD13079 and HD113878 were discovered to exhibitδ Scuti type variability. Photometric variability was alsodis-covered in HD13038, for which the type of peculiarity andvariability is not fully explained. The null results of this survey arealso presented and discussed.
| Studies of chemically peculiar stars
This thesis is on the framework of the "NainiTal-Cape Survey" programmefor searching photometric variability in chemically peculiar stars,initiated in 1997 at the ARIES, NainiTal, India, in collaboration withthe South African Astronomical Observatory, Cape Town and ISRO,Bangalore. This paper presents the corresponding results. The Am starsHD98851, HD102480, HD13079 and HD113878 were discovered to exhibit aScuti type of variability. Photometric variability was also discoveredin HD13038, for which the type of peculiarity and variability is not yetfully explained. The null results obtained in this survey are alsopresented and discussed, as they provide an interesting data referencefor upcoming studies.
| HD 8801: A Unique Single Am Star with γ Doradus and δ Scuti Pulsations
We have discovered the first example of a star pulsating intrinsicallywith both γ Doradus and δ Scuti frequencies. The star, HD8801, is an Am metallic-line star that appears to be single. Since thevast majority of Am stars are members of binary systems with periodsless than 1000 days and also do not pulsate, HD 8801 possesses a veryunusual, if not unique, combination of physical properties. Ourphotometry, acquired with an automatic telescope at FairbornObservatory, resolves six independent pulsation periods between 0.048and 0.404 days. The two longest periods lie within the range of γDor variables, while the four shorter periods are within the range ofδ Sct stars. Eleven radial velocities, obtained over an 11 monthperiod, have a mean of 0.8+/-0.3 km s-1, providing noevidence for a spectroscopic companion. The star is on the main sequenceand lies within both the γ Dor and δ Sct instability strips.Pulsation constants computed for the six periods agree with pulsationconstants computed for other γ Dor and δ Sct variables. HD8801 is also the first confirmed case of a metallic-line star pulsatingwith γ Dor frequencies. Its projected rotational velocity of 55 kms-1 is typical for Am stars, which, as a group, rotate moreslowly than normal A stars. HD 8801's slow rotation compared to normal Astars does not appear to arise from either a binary companion orevolutionary expansion and thus remains a puzzle. The coexistence ofmetallicism and pulsation in several main-sequence stars near the rededge of the δ Sct strip contradicts recent models that predictpulsations only in more evolved stars.
| Discovery of unusual pulsations in the cool, evolved Am stars HD 98851 and HD 102480
The chemically peculiar (CP) stars HD 98851 and HD 102480 have beendiscovered to be unusual pulsators during the `Naini Tal-Cape Survey'programme to search for pulsational variability in CP stars. Time seriesphotometric and spectroscopic observations of these newly discoveredstars are reported here. Fourier analyses of the time series photometryreveal that HD 98851 is pulsating mainly with frequencies 0.208 and0.103 mHz, and HD 102480 is pulsating with frequencies 0.107, 0.156 and0.198 mHz. The frequency identifications are all subject to 1d-1 cycle count ambiguities. We have matched the observedlow-resolution spectra of HD 98851 and HD 102480 in the range 3500-7400Å with theoretical synthetic spectra using Kurucz models withsolar metallicity and a micro-turbulent velocity of 2 km s-1.These yield Teff= 7000 +/- 250 K, log g= 3.5 +/- 0.5 for HD98851 and Teff= 6750 +/- 250 K, log g= 3.0 +/- 0.5 for HD102480. We determined the equivalent H-line spectral class of thesestars to be F1 IV and F3 III/IV, respectively. A comparison of thelocation of HD 98851 and HD 102480 in the HR diagram with theoreticalstellar evolutionary tracks indicates that both stars are about1-Gyr-old, 2-Msolar stars that lie towards the red edge ofthe δ Sct instability strip. From comparison between the observedand calculated physical parameters, we conclude that HD 98851 and HD102480 are cool, evolved Am pulsators. The light curves of thesepulsating stars have alternating high and low amplitudes, nearlyharmonic (or subharmonic) period ratios, high pulsational overtones andAm spectral types. This is unusual for both Am and δ Sctpulsators, making these stars interesting objects for furtherobservational and theoretical studies.
| The 77th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 1152 variable stars recently designated in the system ofthe General Catalogue ofVariable Stars. New designations are alsointroduced for two ``old'' variables whose corrected coordinates bringthem to other constellations.
| Photometry of δ Sct-type and Related Stars: Results of AD Ari, IP Vir and YZ Boo
Photometric results of three δ Scuti stars, AD Ari, IP Vir and YZBoo from new observations obtained at the Xinglong Station of theBeijing Astronomical Observatory (BAO) during 2000 and 2001 arereported. We present here the preliminary analyses. Detailed studies ofthese stars based on additional data will be published separately.
| New pulsating variables discovered from the Naini Tal-Cape survey.
Not Available
| Development of a three channel photometer for UPSO, Naini Tal.
Not Available
| UPSO three channel fast photometer
The design and performance of a modular portable three channel fastphotometer is described. It can be disassembled as single individualchannels such that the system can also be used as a single channelphotometer. The instrument is put into operation since November 1999 onthe 1-m UPSO telescope at Nainital. Since then, it is used extensivelyfor the survey of roAp stars in the northern sky at UPSO. Thediscoveries made using this new photometer are also mentioned.
| Naini Tal-Cape survey for pulsating chemically peculiar stars - A status report
The "Naini Tal-Cape survey for rapidly oscillating Ap stars", to searchthe northern hemi-sphere sky for pulsating stars was initiated in 1997.This is a collaboration between India and South Africa. So far about 70stars have been observed and 4 variables have been discovered. Thevariables are HD 13079, HD 13038, HD 12098 and HD 98851. Of these HD12098 is a likely rapidly oscillating Ap star. This paper gives a statusreport on the survey. The methodology of this survey and an evaluationof observing time vis-a-vis the chance of discovering a new variable arediscussed.
| Discovery of pulsations in HD 98851
Using the UPSO 1-m Sampurnanand reflector telescope equipped with a fastphotometer, we observed the chemically peculiar (CP) star HD 98851 for atotal of around 30 hours on 5 different nights between January to April2000. From the Fourier analysis of our data we have found that HD 98851pulsates with periods of 75.76 min and 151.52 min and amplitudes ? 25mmag and 12 mmag respectively. The star appears to be a ? Scutivariable.
| Discovery of delta Scuti Pulsations in HD 98851
Not Available
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| Photoelectric photometry of stars near the north Galactic pole. II
UBV photometric observations of about 700 stars near the north Galacticpole, obtained using single-channel photometers on the 40-cm and 60-cmCassegrain telescopes at Kvistaberg Observatory (during 1976-1983) andthe Spanish International Observatory (during 1984), respectively, aspart of a program including the stars to be observed by the Hipparcosspacecraft, are reported. The data are presented in a series of tablesand briefly characterized.
| Spectroscopic tests of photoelectric stellar classification of abnormal stars
Spectroscopic classification is obtained for 169 northern A5-G0 starspredicted by Olsen (1979, 1980) to have abnormal spectra on the basis ofStromgren four-color photometry. The success in identifying reddenedearly type stars was nearly 100 percent, for Am and early type weaklined stars about 75 percent, for stars above main sequence about 50percent, for composite spectra about 25 percent, and for Ap and LambdaBoo stars 0 percent. Thus photoelectric photometry is a successful firststep in discovering stars of the more extreme spectroscopicabnormalities.
| Estimation of spectral classifications for bright northern stars with interesting Stromgren indices
The purpose of this investigation is to provide spectroscopic observerswith finding lists of potentially interesting objects. From anunpublished UVBY catalogue of 7026 northern stars (mostly brighter than8.3m) 1094 objects with interesting combinations of UVBY indices havebeen selected. Most stars with post-HD classifications have beenexcluded, as well as late F dwarfs belonging to the intermediatepopulation II. For the 792 remaining stars estimated spectralclassifications are given. The techniques and experience from a previouspaper dealing with southern stars have been utilized here. Among thepredicted spectral classifications are 40 OB stars; 262 Ap, Am, or Fmstars; 16 supergiants of types A to G; 110 bright giants of types A to K(class II); 156 double stars or objects with composite spectra; 26 lateF dwarfs; 91 weak-lined dwarf and giant stars of types F to K, includingearly F-type population II field blue stragglers; and a few possiblefield horizontal branch stars, lambda Bootis-type stars, and late-typehalo giants.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Большая Медведица |
| Прямое восхождение: | 11h22m51.18s |
| Склонение: | +31°49'41.1" |
| Видимая звёздная величина: | 7.415 |
| Расстояние: | 171.233 парсек |
| Собственное движение RA: | -41.4 |
| Собственное движение Dec: | -15.5 |
| B-T magnitude: | 7.818 |
| V-T magnitude: | 7.449 |
Каталоги и обозначения:
|
INHABITED SKY
