G. A. H. Walker

The MOST Asteroseismology Mission: Ultraprecise Photometry from Space

ABSTRACT The Microvariablity and Oscillations of Stars (MOST) mission is a low‐cost microsatellite designed to detect low‐degree acoustic oscillations (periods of minutes) with micromagnitude precision in solar‐type stars and metal‐poor subdwarfs. There are also plans to detect light reflected from giant, short‐period, extrasolar planets and the oscillations of roAp stars and the turbulent variability in the dense winds of Wolf‐Rayet stars. This paper describes the experiment and how we met the challenge of ultraprecise photometry despite severe constraints on the mass, volume, and power available for the instrument. A side‐viewing, 150 mm aperture Rumak‐Maksutov telescope feeds two frame‐transfer CCDs, one for tracking and the other for science. There is a single 300 nm wide filter centered at 525 nm. Microlenses project Fabry images of the brighter ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage...

Speckle Noise and the Detection of Faint Companions

ABSTRACT 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} \usepackage[OT2,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

Hot Jupiters and hot spots: The Short- and long-term chromospheric activity on stars with giant planets

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The Very Low Albedo of an Extrasolar Planet: MOST* Space-based Photometry of HD 209458

\end{document} of residual light in the halo (S being the Strehl ratio of the image). These pre...

The On/Off Nature of Star-Planet Interactions

We monitored the chromospheric activity in the Ca II H and K lines of 13 solar-type stars (including the Sun): 8 of them over 3 years at the Canada-France-Hawaii Telescope (CFHT) and 5 in a single run at the Very Large Telescope (VLT). A total of 10 of the 13 targets have close planetary companions. All of the stars observed at the CFHT show long-term (months to years) changes in H and K intensity levels. Four stars display short-term (days) cyclical activity. For two, HD 73256 and κ1 Cet, the activity is likely associated with an active region rotating with the star; however, the flaring in excess of the rotational modulation may be associated with a hot Jupiter. A planetary companion remains a possibility for κ1 Cet. For the other two, HD 179949 and υ And, the cyclic variation is synchronized to the hot Jupiters orbit. For both stars this synchronicity with the orbit is clearly seen in two out of three epochs. The effect is only marginal in the third epoch at which the seasonal level of chromospheric activity had changed for both stars. Short-term chromospheric activity appears weakly dependent on the mean K line reversal intensities for the sample of 13 stars. In addition, a suggestive correlation exists between this activity and the Mp sin i of the stars hot Jupiter. Because of their small separation (≤0.1 AU), many of the hot Jupiters lie within the Alfven radius of their host stars, which allows a direct magnetic interaction with the stellar surface. We discuss the conditions under which a planets magnetic field might induce activity on the stellar surface and why no such effect was seen for the prime candidate, τ Boo. This work opens up the possibility of characterizing planet-star interactions, with implications for extrasolar planet magnetic fields and the energy contribution to stellar atmospheres.

EVIDENCE FOR PLANET-INDUCED CHROMOSPHERIC ACTIVITY ON HD 179949

Measuring the albedo of an extrasolar planet provides insight into its atmospheric composition and its global thermal properties, including heat dissipation and weather patterns. Such a measurement requires very precise photometry of a transiting system, fully sampling many phases of the secondary eclipse. Space-based optical photometry of the transiting system HD 209458 from the MOST (Microvariablity and Oscillations of Stars) satellite, spanning 14 and 44 days in 2004 and 2005, respectively, allows us to set a sensitive limit on the optical eclipse of the hot exosolar giant planet in this system. Our best fit to the observations yields a flux ratio of the planet and star of -->7 ± 9 ppm (parts per million), which corresponds to a geometric albedo through the MOST bandpass (400-700 nm) of -->Ag = 0.038 ± 0.045. This gives a 1 σ upper limit of 0.08 for the geometric albedo and a 3 σ upper limit of 0.17. HD 209458b is significantly less reflective than Jupiter (for which Ag would be about 0.5). This low geometric albedo rules out the presence of bright reflective clouds in this exoplanets atmosphere. We determine refined parameters for the star and exoplanet in the HD 209458 system based on a model fit to the MOST light curve.

Evidence for a Long-Period Planet Orbiting ϵ Eridani*

Evidence suggestinganobservable magnetic interaction betweenastar and itshot Jupiter appears asacyclic varia- tion of stellar activity synchronized to the planets 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 withESPaDOnSoverafewnightsin2005and2006fromtheCFHT(CaiiHk3968,Kk3933,theCaiiinfraredtriplet (IRT)k8662 line, Hk6563, and He i k5876). Synchronicity of the Ca ii H and K emission of HD 179949 with its planets orbit is clearly seen in four out of six epochs, while rotational modulation with Prot ¼ 7 days is apparent in theothertwoseasons.WeobserveasimilarphenomenononAnd.Thison/off natureof star-planetinteraction(SPI)in the two systems is likely a function of the changing stellar magnetic field structure throughout its activity cycle. Var- iabilityinthetransitingsystemHD 189733islikelyassociatedwithanactiveregionrotatingwiththestar; 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 andBoo leads the subplanetary longitudeby � 70 � .Thetentativecorrelationbetweenthisactivityandtheratioof Mp sin itotheplanetsrotationperiod, aquantityproportionaltothehotJupitersmagneticmoment,firstpresentedbyShkolnikandcoworkersremainsviable. Thisworkfurthersthecharacterizationof SPI,improvingitspotentialasaprobeofextrasolarplanetarymagneticfields. Subject headingg planetary systems — radiation mechanisms: nonthermal — stars: activity — stars: chromospheres — stars: individual (� Boo, HD 179949, HD 209458, HD 189733, HD 217107, HD 149143) — stars: late-type

An Upper Limit on the Albedo of HD 209458b: Direct Imaging Photometry with the MOST Satellite

We have detected the synchronous enhancement of Ca II H and K emission with the short-period planetary orbit in HD 179949. High-resolution spectra taken on three observing runs extending over more than a year show the enhancement coincides with ~ 0 (the sub-planetary point) of the 3.093 day orbit, with the effect persisting for more than 100 orbits. The synchronous enhancement is consistent with planet-induced chromospheric heating by magnetic rather than tidal interaction, but awaits confirmation by further observations. Independent observations are needed to determine whether the stellar rotation is synchronous with the planets orbit. Of the five 51 Peg-type systems monitored, HD 179949 shows the greatest chromospheric H and K activity. Three others show significant nightly variations, but the lack of any phase coherence prevents us saying whether the activity is induced by the planet. Our two standards, τ Ceti and the Sun, show no such nightly variations. Revised periods and updated ephemerides for the planetary orbits are also included.

Narrow Diffuse Interstellar Bands: A Survey with Precise Wavelengths

High-precision radial velocity (RV) measurements spanning the years 1980.8‐2000.0 are presented for the nearby (3.22 pc) K2 V star e Eri. These data, which represent a combination of six independent data sets taken with four different telescopes, show convincing variations with a period of …7 yr. A least-squares orbital solution using robust estimation yields orbital parameters of period yr, velocity amplitude m s 21 , ecP p 6.9 K p 19 centricity , projected companion mass , and semimajor axis

Magnetic cycles of the planet-hosting star τ Bootis

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 σ). We set a 1 σ upper limit on the planet-star flux ratio of 4.88 × 10-5 corresponding to a geometric albedo upper limit in the MOST bandpass (400-700 nm) of 0.25. The corresponding numbers at the 3 σ level are 1.34 × 10-4 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 σ), if the star does not become more intrinsically variable in the meantime.