136 research outputs found
Oscillations on the star Procyon
Stars are sphere of hot gas whose interiors transmit acoustic waves very
efficiently. Geologists learn about the interior structure of Earth by
monitoring how seismic waves propagate through it and, in a similar way, the
interior of a star can be probed using the periodic motions on the surface that
arise from such waves. Matthews et al. claim that the star Procyon does not
have acoustic surface oscillations of the strength predicted. However, we show
here, using ground-based spectroscopy, that Procyon is oscillating, albeit with
an amplitude that is only slightly greater than the noise level observed by
Matthews et al. using spaced-based photometry
Solar-like oscillations of semiregular variables
Oscillations of the Sun and solar-like stars are believed to be excited
stochastically by convection near the stellar surface. Theoretical modeling
predicts that the resulting amplitude increases rapidly with the luminosity of
the star. Thus one might expect oscillations of substantial amplitudes in red
giants with high luminosities and vigorous convection. Here we present evidence
that such oscillations may in fact have been detected in the so-called
semiregular variables, extensive observations of which have been made by
amateur astronomers in the American Association for Variable Star Observers
(AAVSO). This may offer a new opportunity for studying the physical processes
that give rise to the oscillations, possibly leading to further information
about the properties of convection in these stars.Comment: Astrophys. J. Lett., in the press. Processed with aastex and
emulateap
Searching for p-modes in MOST Procyon data: Another view
Photometry of Procyon obtained by the MOST satellite in 2004 has been
searched for p modes by several groups, with sometimes contradictory
interpretations. We explore two possible factors that complicate the analysis
and may lead to erroneous reports of p modes in these data. Two methods are
used to illustrate the role of subtle instrumental effects in the photometry:
time-frequency analysis, and a search for regularly spaced peaks in a Fourier
spectrum based on the echelle diagramme approach. We find no convincing
evidence of a p-mode signal in the MOST Procyon data. We can account for an
apparent excess of power close to the p-mode frequency range and signs of
structure in an echelle diagramme in terms of instrumental effects.Comment: Article accepted, to appear in A&
The non-detection of oscillations in Procyon by MOST: is it really a surprise?
We argue that the non-detection of oscillations in Procyon by the MOST
satellite reported by Matthews et al. (2004) is fully consistent with published
ground-based velocity observations of this star. We also examine the claims
that the MOST observations represent the best photometric precision so far
reported in the literature by about an order of magnitude and are the most
sensitive data set for asteroseismology available for any star other than the
Sun. These statements are not correct, with the most notable exceptions being
observations of oscillations in alpha Cen A that are far superior. We further
disagree that the hump of excess power seen repeatedly from velocity
observations of Procyon can be explained as an artefact caused by gaps in the
data. The MOST observations failed to reveal oscillations clearly because their
noise level is too high, possibly from scattered Earthlight in the instrument.
We did find an excess of strong peaks in the MOST amplitude spectrum that is
inconsistent with a simple noise source such as granulation, and may perhaps
indicate oscillations at roughly the expected level.Comment: 6 pages, accepted for publication in A&A Letter
Asteroseismology of Procyon A with SARG at TNG
We present high precision radial velocity measurements on the F5 IV star
alpha CMi obtained by the SARG spectrograph at TNG (Telescopio Nazionale
Galileo) exploiting the iodine cell technique. The time series of about 950
spectra of Procyon A taken during 6 observation nights are affected by an
individual error of 1.3 m/s. Thanks to the iodine cell technique, the
spectrograph contribution to the Doppler shift measurement error is quite
negligible and our error is dominated by the photon statistics Brown et al
1994. An excess of power between 0.5 and 1.5 mHz, detected also by Martic et
al. 2004 has been found. We determined a large separation frequency Delta nu0 =
56\pm 2 microHz, consistent with both theoretical estimates Chaboyer et al.
1999 and previous observations Martic et al. 2004.Comment: 4 pages, 5 figures, accepted to be published in A&A Letter
Evidence for solar-like oscillations in beta Hydri
We have made a clear detection of excess power, providing strong evidence for
solar-like oscillations in the G2 subgiant beta Hyi. We observed this star over
five nights with the UCLES echelle spectrograph on the 3.9-m Anglo-Australian
Telescope, using an iodine absorption cell as a velocity reference. The time
series of 1196 velocity measurements shows an rms scatter of 3.30 m/s, and the
mean noise level in the amplitude spectrum at frequencies above 0.5 mHz is 0.11
m/s. We see a clear excess of power centred at 1.0 mHz, with peak amplitudes of
about 0.5 m/s, in agreement with expectations for this star. Fitting the
asymptotic relation to the power spectrum indicates the most likely value for
the large separation is 56.2 microHz, also in good agreement with the known
properties of beta Hyi.Comment: Accepted by ApJ Letter
Detection of Solar-like Oscillations in the G7 Giant Star xi Hya
We report the firm discovery of solar-like oscillations in a giant star. We
monitored the star xi Hya (G7III) continuously during one month with the
CORALIE spectrograph attached to the 1.2m Swiss Euler telescope. The 433
high-precision radial-velocity measurements clearly reveal multiple oscillation
frequencies in the range 50 - 130 uHz, corresponding to periods between 2.0 and
5.5 hours. The amplitudes of the strongest modes are slightly smaller than 2
m/s. Current model calculations are compatible with the detected modes.Comment: 4 pages, 4 figures, accepted for publication as a letter in A&
p-mode frequencies in solar-like stars : I. Procyon A
As a part of an on-going program to explore the signature of p-modes in
solar-like stars by means of high-resolution absorption lines pectroscopy, we
have studied four stars (alfaCMi, etaCas A, zetaHer A and betaVir). We present
here new results from two-site observations of Procyon A acquired over twelve
nights in 1999. Oscillation frequencies for l=1 and l=0 (or 2) p-modes are
detected in the power spectra of these Doppler shift measurements. A frequency
analysis points out the dificulties of the classical asymptotic theory in
representing the p-mode spectrum of Procyon A
Asteroseismology of Procyon with SOPHIE
This paper reports a 9-night asteroseismic observation program conducted in
January 2007 with the new spectrometer Sophie at the OHP 193-cm telescope, on
the F5 IV-V target Procyon A. This first asteroseismic program with Sophie was
intended to test the performance of the instrument with a bright but demanding
asteroseismic target and was part of a multisite network. The Sophie spectra
have been reduced with the data reduction software provided by OHP. The Procyon
asteroseismic data were then analyzed with statistical tools. The asymptotic
analysis has been conducted considering possible curvature in the echelle
diagram analysis. These observations have proven the efficient performance of
Sophie used as an asteroseismometer, and succeed in a clear detection of the
large spacing. An \'echelle diagram based on the 54-Hz spacing shows clear
ridges. Identification of the peaks exhibits large spacings varying from about
52 Hz to 56 Hz.Comment: 7 pages, 7 figure
- …