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On the spectroscopic nature of the cool evolved Am star HD151878
Recently, Tiwari, Chaubey & Pandey detected the bright component ofthe visual binary HD151878 to exhibit rapid photometric oscillationsthrough a Johnson B filter with a period of 6min (2.78mHz) and a high,modulated amplitude up to 22mmag peak-to-peak, making this star by farthe highest amplitude rapidly oscillating Ap (roAp) star known. As a newroAp star, HD151878 is of additional particular interest as a scarceexample of the class in the northern sky, and only the second known caseof an evolved roAp star - the other being HD116114. We used theFIbre-fed Echelle Spectrograph at the Nordic Optical Telescope to obtainhigh time-resolution spectra at high dispersion to attempt to verify therapid oscillations. We show here that the star at this epoch isspectroscopically stable to rapid oscillations of no more than a fewtens of ms-1. The high-resolution spectra furthermore showthe star to be of type Am rather than Ap and we show the star lacks mostof the known characteristics for roAp stars. We conclude that this is anAm star that does not pulsate with a 6-min period. The originaldiscovery of pulsation is likely to be an instrumental artefact.Based on observations collected at the Nordic Optical Telescope as partof programme 36-418. E-mail: lfreyham@gmail.com
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| HD12098 and Other Results from Nainital-Cape Survey
Nainital-Cape Survey was started with an aim to search for new rapidlyoscillating Ap stars in the northern hemisphere. We discovered one newmono-periodic roAp star HD12098. The frequency separation of HD12098suggests a rotation period of 5.5 days for the star. We summarize herethe observations of HD12098 and briefly discuss the results of themulti-site observation campaign organized to resolve the ambiguity inthe determination of the rotation period of HD12098. Other interestingresults like non-oscillating Ap stars discovered and two candidate starsin which roAp periodicity is seen but not confirmed are also discussed.
| 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
| Lists of photometric AM candidates
The Geneva photometric m parameter (Nicolet and Cramer, 1982) is used inorder to select Am photometric candidates from the Rufener (1981)catalogue. Two lists are given, the first containing field stars and thesecond cluster stars. According to the photometric criteria thediffusion process probably responsible for the Am phenomenon takes placerather quickly as Am candidates are present in young clusters. It isconfirmed that the phenomenon is enhanced by low rotational velocity andhigh metallicity. The age seems to slightly affect the Am phenomenon.
| Classification spectrale d'etoiles AP et Am.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975A&AS...21...25F&db_key=AST
| Multicolor photometry of metallic-line stars. III. A photometric catalogue
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974RMxAA...1..175M&db_key=AST
| Slit Spectra of Some Peculiar and Metallic-Line A Stars
Not Available
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Наблюдательные данные и астрометрия
| Созвездие: | Лебедь |
| Прямое восхождение: | 21h48m16.05s |
| Склонение: | +54°23'14.6" |
| Видимая звёздная величина: | 7.846 |
| Расстояние: | 127.226 парсек |
| Собственное движение RA: | 37.6 |
| Собственное движение Dec: | 31.3 |
| B-T magnitude: | 8.144 |
| V-T magnitude: | 7.871 |
Каталоги и обозначения:
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