136 research outputs found
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 been
discovered to be unusual pulsators during the ``Naini Tal Cape Survey''
programme to search for pulsational variability in CP stars. Time series
photometric and spectroscopic observations of these newly discovered stars are
reported here. Fourier analyses of the time series photometry reveal that HD
98851 is pulsating mainly with frequencies 0.208 mHz and 0.103 mHz, and HD
102480 is pulsating with frequencies 0.107 mHz, 0.156 mHz and 0.198 mHz. The
frequency identifications are all subject to 1 d cycle count
ambiguities. We have matched the observed low resolution spectra of HD 98851
and HD 102480 in the range 3500-7400 \AA with theoretical synthetic spectra
using Kurucz models with solar metallicity and a micro-turbulent velocity 2 km
s. These yield K, log for HD 98851
and K, log for HD 102480. We
determined the equivalent H-line spectral class of these stars to be F1 IV and
F3 III/IV, respectively. A comparison of the location of HD 98851 and HD 102480
in the HR diagram with theoretical stellar evolutionary tracks indicates that
both stars are about 1-Gyr-old, 2- stars that lie towards the red
edge of the Sct instability strip. We conclude that HD 98851 and HD
102480 are cool, evolved Am pulsators. The light curves of these pulsating
stars have alternating high and low amplitudes, nearly harmonic (or
sub-harmonic) period ratios, high pulsational overtones and Am spectral types.
This is unusual for both Am and Sct pulsators, making these stars
interesting objects.Comment: 9 pages, 6 Figures, Accepted for publication in MNRA
Evolution of the optical spectrum of SN 1987a in the large magellanic cloud
The evolution of the spectrum of SN1987a is traced from 1987 February 26 to March 31. Based on the low-resolution spectroscopic data we identify the lines of H, He I, Na I, Fe II, Sc II, Ca II which are known to be present in Type II Supernovae, and also present evidence for the existence of lines of Mg I, CaI, O I, and N I. We discuss the evolution of the Hα profile, and draw attention to its complex structure around March 30. Close to the rest wavelength of Ha a double-peaked structure appeared in the profile with a peak-to-peak separation of ~ 1400 km s−1, suggestive of an expanding shell or disc of gas. Using the available broadband photometric information, we also trace the evolution of the photosphere of SN1987a assuming that it radiates like a supergiant
A spectroscopic analysis of the chemically peculiar star HD207561
In this paper we present a high-resolution spectroscopic analysis of the
chemically peculiar star HD207561. During a survey programme to search for new
roAp stars in the Northern hemisphere, Joshi et al. (2006) observed significant
photometric variability on two consecutive nights in the year 2000. The
amplitude spectra of the light curves obtained on these two nights showed
oscillations with a frequency of 2.79 mHz [P~6-min]. However, subsequent
follow-up observations could not confirm any rapid variability. In order to
determine the spectroscopic nature of HD207561, high-resolution spectroscopic
and spectro-polarimetric observations were carried out. A reasonable fit of the
calculated Hbeta line profile to the observed one yields the effective
temperature (Teff) and surface gravity (log g) as 7300 K and 3.7 dex,
respectively. The derived projected rotational velocity (vsin i) for HD207561
is 74 km/sec indicative of a relatively fast rotator. The position of HD207561
in the H-R diagram implies that this is slightly evolved from the main-sequence
and located well within the delta-Scuti instability strip. The abundance
analysis indicates the star has slight under-abundances of Ca and Sc and mild
over-abundances of iron-peak elements. The spectro-polarimetric study of
HD207561 shows that the effective magnetic field is within the observational
error of 100 gauss (G). The spectroscopic analysis revealed that the star has
most of the characteristics similar to an Am star, rather than an Ap star, and
that it lies in the delta-Scuti instability strip; hence roAp pulsations are
not expected in HD207561, but low-overtone modes might be excited.Comment: 8 pages, 7 figures, 3 tables. Accepted for pubblication in MNRA
HD 12098 -A new northern hemisphere roAp star
We present the analysis of 65 hours of high speed photometric observations of HD 12098 taken from State Observatory, Naini Tal and Gurushikhar Observatory, Mt. Abu on sixteen nights spanning from November 1999 to November 2000. HD 12098 is the first rapidly oscillating Ap star discovered from the "Naini Tal-Cape survey for northern hemisphere roAp stars". It is the 32nd in the complete list. HD 12098 exhibits one predominant mode of oscillation a
The Naini Tal -Cape survey for pulsations in chemically peculiarA-type stars: I. Methods and preliminary results
A new survey for pulsating, chemically peculiar A- and F-type stars in the northern hemisphere has been initiated using the 1-m telescope at Uttar Pradesh State Observatory in Naini Tal. The survey is primarily structured to reveal high-overtone pulsations in chemically peculiar A-F stars, but it is also revealing low-overton
Discovery of pulsations in the Am star HD 13079
Pulsation in cool main-sequence Am stars is a rare phenomenon observed in a few marginal Am stars and only one classical Am star. The chemically peculiar star HD 13079 is shown to be pulsating with a 78-min period and a peak-to-peak B amplitude of 0.02 mag. The Hipparcos parallax, uvbyβ photometry and pulsations together suggest that HD 13079 is an Am star near the zero-age main sequence, and that it is a fundamental-mode pulsator on the red edge of the instability strip
The Nainital-Cape Survey -- II:Report for pulsation in five chemically peculiar A-type stars and presentation of 140 null results
To search photometric variability in chemically peculiar A type stars in the
northern hemisphere. High-speed photometric observations of Ap and Am star
candidates have been carried out from ARIES (Manora Peak, Nainital) using a
three-channel fast photometer attached to the ARIES 104-cm Sampurnanand
telescope. This paper presents three new variables: HD 113878, HD 118660 and HD
207561. During the time span of the survey (1999 December to 2004 January)
pulsations of the Sct type were also found for the two evolved Am
stars HD 102480 and HD 98851, as reported in Joshi et al. (2002, 2003).
Additionally, we present 140 null results of the survey for this time span. The
star HD 113878 pulsates with a period of 2.31 hr, which is typical of
Sct stars. HD 118660 exhibits multi-periodic variability with a prominent
period of nearly 1 hr. These periods need to be investigated and make HD 118660
a particularly interesting target for further observations. For HD 207561, a
star classified as Am, a probable pulsation with a period of 6 min was found in
the light curves obtained on two consecutive nights. Both HD 102480 and HD
98851 exhibit unusual alternating high and low amplitude maxima, with a period
ratio of 2:1. The analysis of the null results confirms the photometric quality
of the NainitalComment: 14 pages, 13 figures, Accepted for publication in A&
UPSO three channel fast photometer
The design and performance of a modular portable three channel fast photometer is described. It can be disassembled as single individual channels such that the system can also be used as a single channel photometer. The instrument is put into operation since November 1999 on the 1-m UPSO telescope at Nainital. Since then, it is used extensively for the survey of roAp stars in the northern sky at UPSO. The discoveries made using this new photometer are also mentioned
High speed photometry of PG 1012-029
High speed optical photometric observations of PG 1012-029, conducted during 1990-1991, confirm the nova-like classification of the object. Several eclipses observed by us have been used to refine the orbital period of the system. Variations in the light curves and in particular, the presence of a bright hot spot in our 1991 data are high-lighted. We also deduce a maximum mass transfer rate of 1.5 10-8M⊙ yr-1 for the system
HD 12098, the new far-Northern roAp star
The rapidly oscillating Ap (roAp) stars are cool, magnetic, chemically peculiar stars which pulsate in non-radial p-modes in the period range 4-16 min and have Johnson B amplitudes less than 8 mmag. "The NainiTal-Cape survey" to search for and study new roAp stars in the northern hemisphere was initiated in 1998 in collaboration between ISAC & UPSO from India and SAAO & UCT from South Africa. HD12098 is the first roAp star discovered in this survey and also the first far northern hemisphere roAp star. During the initial observations the star showed modulation in the pulsation amplitude indicating the multi-periodicity of pulsations. The multi-periodicity may be either due to the excitation of different modes or due to the rotation of the star. In order to resolve these frequencies HD12098 was observed extensively in October 2000. The preliminary results of these observations are presented here
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