235 research outputs found
Radial Velocity Variations in Pulsating Ap Stars III. The Discovery of 16.21 min Oscillations in Beta CrB
We present the analysis of 3 hrs of a rapid time series of precise stellar
radial velocity (RV) measurements (sigma = 4.5 m/s) of the cool Ap star Beta
CrB. The integrated RV measurements spanning the wavelength interval 5000-6000
Ang. show significant variations (false alarm probability = 10^-5) with a
period of 16.21 min (nu = 1028.17 micro Hz) and an amplitude of 3.54 +/- 0.56
m/s. The RV measured over a much narrower wavelength interval reveals one
spectral feature at 6272 Ang. pulsating with the same 16.21 min period and an
amplitude of 138 +/- 23 m/s. These observations establish Beta CrB to be a
low-amplitude rapidly oscillating Ap star.Comment: 5 Pages, 5 figure
Detection of an exoplanet around the evolved K giant HD 66141
Aims. We have been carrying out a precise radial velocity (RV) survey for K
giants to search for and study the origin of the lowamplitude and long-periodic
RV variations.
Methods. We present high-resolution RV measurements of the K2 giant HD 66141
from December 2003 to January 2011 using the fiber-fed Bohyunsan Observatory
Echelle Spectrograph (BOES) at Bohyunsan Optical Astronomy Observatory (BOAO).
Results. We find that the RV measurements for HD 66141 exhibit a periodic
variation of 480.5 +/- 0.5 days with a semi-amplitude of 146.2 +/- 2.7 m/s. The
Hipparcos photometry and bisector velocity span (BVS) do not show any obvious
correlations with RV variations. We find indeed 706.4 +/- 35.0 day variations
in equivalent width (EW) measurements of H_alpha line and 703.0 +/- 39.4 day
variations in a space-born measurements 1.25{\mu} flux of HD 66141 measured
during COBE/DIRBE experiment. We reveal that a mean value of long-period
variations is about 705 +/- 53 days and the origin is a rotation period of the
star and variability that is caused by surface inhomogeneities. For the 480 day
periods of RV variations an orbital motion is the most likely explanation.
Assuming a stellar mass of 1.1 +/- 0.1 M_Sun? for HD 66141, we obtain a minimum
mass for the planetary companion of 6.0 +/- 0.3 M_Jup with an orbital
semi-major axis of 1.2 +/- 0.1 AU and an eccentricity of 0.07 +/- 0.03.Comment: 7 pages, 10 figures, 3 tables, accepted for publisation in Astronomy
& Astrophysic
Accretion and outflow activity on the late phases of pre-main-sequence evolution. The case of RZ Piscium
RZ Psc is an isolated high-latitude post-T Tauri star that demonstrates a UX
Ori-type photometric activity. The star shows very weak spectroscopic
signatures of accretion, but at the same time possesses the unusual footprints
of the wind in Na I D lines. In the present work we investigate new
spectroscopic observations of RZ Psc obtained in 2014 during two observation
runs. We found variable blueshifted absorption components (BACs) in lines of
the other alcali metals, K I 7699 \AA\ and Ca II IR triplet. We also confirmed
the presence of a weak emission component in the H line, which allowed
us to estimate the mass accretion rate on the star as Msun yr. We could not reveal any clear periodicity in the
appearance of BACs in sodium lines. Nevertheless, the exact coincidence of the
structure and velocities of the Na I D absorptions observed with the interval
of about one year suggests that such a periodicity should exist
Detection of a delta Scuti-type pulsating component in the detached eclipsing binary system TU CMa
We report the detection of 30.5 min low-amplitude (A=0.003 mag) delta Scuti-type pulsations in an A5V-A7V type component of the detached eclipsing binary system TU CMa
Evaluation of the professional teaching competence: chinese experience
The article describes the rules and procedures for hiring and evaluating the professional competence of teachers on the example ofChina, where there is a system for evaluating the professional competence of teachers
Spectroscopic Devices for Asteroseismology With Small Telescopes in NARIT
The National Astronomical Research Institute of Thailand (NARIT) has a
manifold network of small telescopes installed worldwide. These telescopes
serve educational and research purposes and are equipped mainly with CCD
detectors for direct imaging and photometry. To extend the possible field of
applications, several telescopes were fitted with commercially available
medium-resolution spectrographs eShel from Shelyak. With these devices,
researchers in NARIT obtained a versatile tool for stellar spectroscopy. Here
we describe the current status of available equipment, possible ways of
upgrading, and briefly introduce the achieved results of the asteroseismologic
study of fast-rotating stars.Comment: This paper was submitted as a contribution to the proceedings of the
third Belgo-Indian Network for Astronomy and Astrophysics (BINA) workshop,
which was held in Bhimtal, Uttarakhand (India) on 22-24 March 2023. The
final, peer-reviewed version will be published in Bulletin de la Soci\'et\'e
Royale des Sciences de Li\`ege. The manuscript contains 5 pages, 3 figures,
and 4 reference
Radial Velocity Variations in Pulsating Ap Stars. II. 33 Librae
We present precise relative radial velocity (RV) measurements for the rapidly
oscillating Ap (roAp) star 33 Librae measured from high resolution data
spanning the wavelength interval 5000--6200 A. We find that pulsational radial
velocity amplitude determined over a broad wavelength range (~100 A) depends on
the spectral region that is examined and can be as high as 60 m/s at 5600 A and
as low as 7 m/s in the 5900 A region. RV measurements of individual spectral
lines can show even higher RV amplitudes. The acoustic cross-sections of the
atmosphere, i.e. the phase and amplitude of the pulsations, as a function of
optical depth is found for spectral lines of Ca, Cr, Fe, La, Ce, Gd, Er and Nd.
This analysis shows that pulsation phase is variable through the atmosphere and
that Nd III lines pulsate almost 180 degrees out-of-phase with those of Nd II
features and are formed significantly higher in the stellar atmosphere. This
conclusively establishes the presence of at least one radial node to the
pulsations in the upper stellar atmosphere. The histogram of pulsational phases
for all individual spectral feature shows a bi-modal Gaussian distribution with
17% of the lines having a pulsational phase approximatels 165 degrees
out-of-phase with most other spectral lines. This is also consistent with the
presence of a radial node in the stellar atmosphere. The accumulation of phase
due to a running wave component can explain the 165 degree phase difference as
well as the broader width (by a factor of two) of one of the Gaussian
components of the phase distribution.Comment: 18 pages, 12 Figures, accepted by MNRA
Pulsations in the atmosphere of the roAp star HD 24712 II. Theoretical models
We discuss pulsations of the rapidly oscillating Ap (roAp) star HD 24712 (HR
1217) based on nonadiabatic analyses taking into account the effect of dipole
magnetic fields. We have found that all the pulsation modes appropriate for HD
24712 are damped; i.e., the kappa-mechanism excitation in the hydrogen
ionization layers is not strong enough to excite high-order p-modes with
periods consistent with observed ones, all of which are found to be above the
acoustic cut-off frequencies of our models.
The main (2.721 mHz) and the highest (2.806 mHz) frequencies are matched with
modified and modes, respectively. The large frequency separation
(Hz) is reproduced by models which lay within the error box of
HD 24712 on the HR diagram. The nearly equally spaced frequencies of HD 24712
indicate the small frequency separation to be as small as Hz.
However, the small separation derived from theoretical and 2 modes are
found to be larger than Hz. The problem of equal spacings could be
resolved by assuming that the spacings correspond to pairs of and
modes. The amplitude distribution on the stellar surface is strongly affected
by the magnetic field resulting in the predominant concentration at the polar
regions.
Amplitudes and phases of radial-velocity variations for various spectral
lines are converted to relations of amplitude/phase versus optical depth in the
atmosphere. Oscillation phase delays gradually outward in the outermost layers
indicating the presence of waves propagating outward. The phase changes steeply
around , which supports a relation having a small
temperature inversion there.Comment: 11 pages, 13 figures, accepted for publication in MNRA
- …