The On/Off Nature of Star-Planet Interactions Shkolnik, Evgenya; Bohlender, David A; Walker, Gordon A. H ...
Astrophysical journal/The Astrophysical journal,
03/2008, Letnik:
676, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Evidence suggesting an observable magnetic interaction between a star and its hot Jupiter appears as a cyclic variation of stellar activity synchronized to the planet's orbit. In this study we ...monitored the chromospheric activity using several stellar activity indicators of seven stars with hot Jupiters using new high-resolution echelle spectra collected with ESPaDOnS over a few nights in 2005 and 2006 from the CFHT (Ca ii H lambda3968, K lambda3933, the Ca ii infrared triplet IRT lambda8662 line, H alpha lambda6563, and He i lambda5876). Synchronicity of the Ca ii H and K emission of HD 179949 with its planet's orbit is clearly seen in four out of six epochs, while rotational modulation with image is apparent in the other two seasons. We observe a similar phenomenon on upsilon And. This on/off nature of star-planet interaction (SPI) in the two systems is likely a function of the changing stellar magnetic field structure throughout its activity cycle. Variability in the transiting system HD 189733 is likely associated with an active region rotating with the star; however, the flaring in excess of the rotational modulation may be associated with its hot Jupiter. As for HD 179949, the peak variability as measured by the mean absolute deviation (MAD) for both HD 189733 and tau Boo leads the subplanetary longitude by image70 degree . The tentative correlation between this activity and the ratio of image to the planet's rotation period, a quantity proportional to the hot Jupiter's magnetic moment, first presented by Shkolnik and coworkers remains viable. This work furthers the characterization of SPI, improving its potential as a probe of extrasolar planetary magnetic fields.
Highly precise and nearly uninterrupted optical photometry of the RR Lyrae star AQ Leo was obtained with the MOST (Microvariability and Oscillations of Stars) satellite over 34.4 d in 2005 ...February–March. AQ Leo was the first known double-mode RR Lyrae pulsator (RRd star). Three decades after its discovery, MOST observations have revealed that AQ Leo oscillates with at least 42 frequencies, of which 32 are linear combinations (up to the sixth order) of the radial fundamental mode and its first overtone. Evidence for period changes of these modes is found in the data. The other intrinsic frequencies may represent an additional non-radial pulsation mode and its harmonics (plus linear combinations) which warrant theoretical modelling. The unprecedented number of frequencies detected with amplitudes down to mmag precision also presents an opportunity to test non-linear theories of mode growth and saturation in RRd stars.
Microvariability & Oscillations of STars (MOST) and All Sky Automated Survey (ASAS) observations have been used to characterize photometric variability of TW Hya on time-scales from a fraction of a ...day to 7.5 weeks and from a few days to 8 yr, respectively. The two data sets have very different uncertainties and temporal coverage properties and cannot be directly combined, nevertheless, they suggest a global variability spectrum with ‘flicker-noise’ properties, that is with amplitudes , over >4 decades in frequency, in the range f= 0.0003–10 c d−1. A 3.7 d period is clearly present in the continuous 11 d, 0.07 d time resolution, observations by MOST in 2007. Brightness extrema coincide with zero-velocity crossings in periodic (3.56 d) radial-velocity variability detected in contemporaneous spectroscopic observations of Setiawan et al. and interpreted as caused by a planet. The 3.56/3.7 d periodicity was entirely absent in the second, 4 times longer MOST run in 2008, casting doubt on the planetary explanation. Instead, a spectrum of unstable single periods within the range of 2–9 d was observed; the tendency of the periods to progressively shorten was well traced using the wavelet analysis. The evolving periodicities and the overall flicker-noise characteristics of the TW Hya variability suggest a combination of several mechanisms, with the dominant ones probably related to the accretion processes from the disc around the star.
Pressure-driven (p-mode) oscillations at the surface of the Sun, resulting from sound waves travelling through the solar interior, are a powerful probe of solar structure, just as seismology can ...reveal details about the interior of the Earth. Astronomers have hoped to exploit p-mode asteroseismology in Sun-like stars to test detailed models of stellar structure and evolution, but the observations are extremely difficult. The bright star Procyon has been considered one of the best candidates for asteroseismology, on the basis of models and previous reports of p-modes detected in ground-based spectroscopy. Here we present a search for p-modes in 32 days of nearly continuous photometric satellite-based observations of Procyon. If there are p-modes in Procyon, they must have lifetimes less than 2-3 days and/or peak amplitudes <15 parts per million, which defy expectations from the Sun's oscillations and previous theoretical predictions. Target selection for future planned asteroseismology space missions may need to be reconsidered, as will the theory of stellar oscillations.
Because the laboratory gas-phase electronic spectra of only the three polyatomic bare carbon chains C sub(3), C sub(4) and C sub(5) are available, we have made a further attempt to detect the origin ...bands of C sub(4) (3789 Aa) and C sub(5) (5109 Aa) in the diffuse cloud toward zeta Oph. The measurements provide an improved 3 capital sigma limit to their column densities: N(C sub(4)) < 5 x 10 super(11) cm super(-2) and N(C sub(5)) < 1 x 10 super(11) cm super(-2), with a signal-to-noise ratio (S/N) of 42,000 and 31,000 Aa super(-1), respectively, at a resolution of 110,000. The limits to N(C sub(4)) and N(C sub(5)) are lower than predictions from the chemical model used by Roueff and coworkers for such diffuse clouds. In conjunction with observations of related, hydrogen-containing polar chains in the millimeter region and laboratory studies of the electronic transitions of a number of homologous series, these results lead to interesting conclusions about the role of carbon chains as potential carriers of the diffuse interstellar bands (DIBs). First, the abundance and oscillator strength of smaller chains, say up to 10 atoms, are too small to account for the stronger DIBs. Second, because of the electronic configurations of these open-shell species, the lowest energy pi-pi transition does not have a large oscillator strength but the higher energy one in the UV does, and the chains would have to be prohibitively long for these absorptions to shift into the DIB 4000-9000 Aa wavelength region. The exceptions are closed-shell systems such as the odd-numbered bare carbon chains, and the ones in the C sub(15)-C sub(31) size range that have their very strong transitions in this region. These species should be a major goal for laboratory and subsequent astronomical studies.
We report on the measurement of transit times for the HD 209458 planetary system from photometry obtained with the MOST (Microvariability and Oscillations of Stars) space telescope. Deviations from a ...constant orbital period can indicate the presence of additional planets in the system that are yet undetected, potentially with masses approaching an Earth mass. The MOST data sets of HD 209458 from 2004 and 2005 represent unprecedented time coverage with nearly continuous observations spanning 14 and 43 days and monitoring three transits and 12 consecutive transits, respectively. The transit times that we obtain show no variations on three scales: (1) no long- term change in P since before 2004 at 25 ms level, (2) no trend in transit timings during the 2005 run, and (3) no individual transit timing deviations above 80 s level. Together with previously published transit times from Agol & Steffen, this allows us to place limits on the presence of additional close-in planets in the system, in some cases down to below an Earth mass. This result, along with previous radial velocity work, now eliminates the possibility that a perturbing planet could be responsible for the additional heat source needed to explain HD 209458b's anomalous low density.
We present space-based photometry of the transiting exoplanetary system HD 209458 obtained with the Microvariablity and Oscillations of Stars (MOST) satellite, spanning 14 days and covering 4 ...transits and 4 secondary eclipses. The HD 209458 photometry was obtained in MOSTs lower precision direct imaging mode, which is used for targets in the brightness range 6.5 . V . 13. We describe the photometric reduction techniques for this mode of observing, in particular the corrections for stray earthshine. We do not detect the secondary eclipse in the MOST data, to a limit in depth of 0.053 mmag (1 s). We set a 1 s upper limit on the planet-star flux ratio of 4.88 x 10 super(-5) corresponding to a geometric albedo upper limit in the MOST bandpass (400-700 nm) of 0.25. The corresponding numbers at the 3 s level are 1.34 x 10 super(-4) and 0.68, respectively. HD 209458b is half as bright as Jupiter in the MOST bandpass. This low geometric albedo value is an important constraint for theoretical models of the HD 209458b atmosphere, in particular ruling out the presence of reflective clouds. A second MOST campaign on HD 209458 is expected to be sensitive to an exoplanet albedo as low as 0.13 (1 s), if the star does not become more intrinsically variable in the meantime.
Speckle Noise and the Detection of Faint Companions Racine, René; Walker, Gordon A. H.; Nadeau, Daniel ...
Publications of the Astronomical Society of the Pacific,
05/1999, Letnik:
111, Številka:
759
Journal Article
Recenzirano
Odprti dostop
Speckles dominate shot noise within the halo of adaptively corrected bright star images and, consequently, impose severe limits on ground‐based attempts to directly detect planets around nearby ...stars. The effect is orders of magnitude greater than conventional photon noise. It depends on the dwell time of the speckle pattern, the brightness of the star, and the fraction
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackageOT2,OT1{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $( 1-S) $ \end{document}
of residual light in the halo (Sbeing the Strehl ratio of the image). These predictions agree well with limits found using the Canada‐France‐Hawaii Telescope adaptive optics bonnette. The limiting brightness for detection is proportional to
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackageOT2,OT1{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $( 1-S) / S$ \end{document}
, emphasizing the need for large Strehl ratios. Strategies to reduce speckle noise are proposed; the encouraging results of a test are presented.
PDF
