Frequency Analysis Of The Rapidly Oscillating Ap Star Hd 60435

The rapidly oscillating Ap (roAp) star HD 60435 has been monitored in a programme of rapid Johnson B photometry during which approximately 355 hours of observations were collected from the Las Campanas, Cerro Tololo Inter-American and South African Astronomical Observatories in two coordinated campaigns from January 1984 to March 1985.;Fourier analysis of these data indicate that the star undergoes oscillations in a spectrum of nearly equally spaced frequencies, corresponding to a range of periods from about 12 to 20 minutes. Typical amplitudes are only a few millimagnitudes. The dominant oscillations occur near a frequency of 1.4 mHz (P {dollar}\simeq{dollar} 12 min). Fourier peaks at frequencies near 2.8 and 3.6 mHz have also been detected sporadically; these may be 2:1 and 3:1 resonances with the 1.4 mHz oscillation, or harmonics produced by the frequency analysis.;Comparison of the overall frequency pattern to the asymptotic theory of nonradial acoustic pulsation has led to the identification of the oscillations as a series of high-overtone (13 {dollar}\le n \le{dollar} 28) p -modes of degree {dollar}\ell{dollar} = 1 and 2. The fundamental frequency spacing {dollar}\nu\sb{lcub}\rm o{rcub} \simeq{dollar} 52 {dollar}\mu{dollar}Hz is consistent with a slightly evolved late A star whose radius is 2.2 {dollar}\pm{dollar} 0.3 R{dollar}\sb\odot{dollar}, as are the results of the classification spectra and Stromgren multi-colour photometry of the star.;The amplitudes of the dominant oscillations are modulated over a long timescale near 8 days, and also show rapid modulation in only a few hours. The latter is primarily due to beating among the many frequencies present in HD 60435, but there is also evidence of actual growth and decay of pulsation modes in less than a day.;The rotation period of HD 60435, based on the star\u27s long-term light curve, is 7.6662 {dollar}\pm{dollar} 0.0001 days. This agrees with the modulation period of the oscillations, as is predicted by the oblique pulsator model for the roAp variables. Application of a dynamical version of this model to the fine splitting observed in the Fourier spectrum of the oscillations places constraints on the magnetic field geometry, predicts that the field should exhibit polarity reversal, and suggests that HD 60435 may have a relatively weak internal field compared to other roAp stars

NESS: Using a Microsatellite to Search For and Track Satellites and Asteroids

The Near Earth Space Surveillance (NESS) mission is being developed by Dynacon and a team of asteroid scientists, supported by the Canadian Space Agency (CSA) and the Canadian Department of National Defence (DND). NESS uses a single satellite to perform a dual mission: searching for an tracking Earth-approaching asteroids, and tracking satellites in Earth orbit. There are aspects of both of these activities that are best accomplished using an orbiting observatory. The concept presented here is to implement NESS using a small imaging telescope mounted on a lowcost microsatellite-class platform, based on the design developed for the MOST stellar photometry microsatellite mission

A combined spectroscopic and photometric stellar activity study of Epsilon Eridani

We present simultaneous ground-based radial velocity (RV) measurements and space-based photometric measurements of the young and active K dwarf Epsilon Eridani. These measurements provide a data set for exploring methods of identifying and ultimately distinguishing stellar photospheric velocities from Keplerian motion. We compare three methods we have used in exploring this data set: Dalmatian, an MCMC spot modeling code that fits photometric and RV measurements simultaneously; the FF$'$ method, which uses photometric measurements to predict the stellar activity signal in simultaneous RV measurements; and H$\alpha$ analysis. We show that our H$\alpha$ measurements are strongly correlated with photometry from the Microvariability and Oscillations of STars (MOST) instrument, which led to a promising new method based solely on the spectroscopic observations. This new method, which we refer to as the HH$'$ method, uses H$\alpha$ measurements as input into the FF$'$ model. While the Dalmatian spot modeling analysis and the FF$'$ method with MOST space-based photometry are currently more robust, the HH$'$ method only makes use of one of the thousands of stellar lines in the visible spectrum. By leveraging additional spectral activity indicators, we believe the HH$'$ method may prove quite useful in disentangling stellar signals

A stable quasi-periodic 4.18 d oscillation and mysterious occultations in the 2011 MOST light curve of TWHya

We present an analysis of the 2011 photometric observations of TW Hya by the MOST satellite; this is the fourth continuous series of this type. The large-scale light variations are dominated by a strong, quasi-periodic 4.18 d oscillation with superimposed, apparently chaotic flaring activity; the former is most likely produced by stellar rotation with one large hot spot created by a stable accretion funnel in the stable regime of accretion while the latter may be produced by small hot spots, created at moderate latitudes by unstable accretion tongues. A new, previously unnoticed feature is a series of semi-periodic, well defined brightness dips of unknown nature of which 19 were observed during 43 days of our nearly-continuous observations. Re-analysis of the 2009 MOST light curve revealed the presence of 3 similar dips. On the basis of recent theoretical results, we tentatively conclude that the dips may represent occultations of the small hot spots created by unstable accretion tongues by hypothetical optically thick clumps.Comment: Printed in MNRA

Photometric variability in FU Ori and Z CMa as observed by MOST

Photometric observations obtained by the MOST satellite were used to characterize optical small scale variability of the young stars FU Ori and Z CMa. Wavelet analysis for FU Ori reveals the possible existence of several 2-9 d quasi-periodic features occurring nearly simultaneously; they may be interpreted as plasma parcels or other localized disc heterogeneities revolving at different Keplerian radii in the accretion disc. Their periods may shorten slowly which may be due to spiralling in of individual parcels toward the inner disc radius, estimated at 4.8+/-0.2 R_sun. Analysis of additional multicolour data confirms the previously obtained relation between variations in the B-V colour index and the V magnitude. In contrast to the FU Ori results, the oscillation spectrum of Z CMa does not reveal any periodicities with the wavelet spectrum possibly dominated by outburst of the Herbig Be component.Comment: Accepted by MNRA

Scattered Light from Close-in Extrasolar Planets: Prospects of Detection with the MOST Satellite

The ultra-precise photometric space satellite MOST (Microvariability and Oscillations of STars) will provide the first opportunity to measure the albedos and scattered light curves from known short-period extrasolar planets. Due to the changing phases of an extrasolar planet as it orbits its parent star, the combined light of the planet-star system will vary on the order of tens of micromagnitudes. The amplitude and shape of the resulting light curve is sensitive to the planet's radius and orbital inclination, as well as the composition and size distribution of the scattering particles in the planet's atmosphere. To predict the capabilities of MOST and other planned space missions, we have constructed a series of models of such light curves, improving upon earlier work by incorporating more realistic details such as: limb darkening of the star, intrinsic granulation noise in the star itself, tidal distortion and back-heating, higher angular resolution of the light scattering from the planet, and exploration of the significance of the angular size of the star as seen from the planet. We use photometric performance simulations of the MOST satellite, with the light curve models as inputs, for one of the mission's primary targets, $\tau$ Bo\"otis. These simulations demonstrate that, even adopting a very conservative signal detection limit of 4.2 $\mu$mag in amplitude (not power), we will be able to either detect the $\tau$ Bo\"otis planet light curve or put severe constraints on possible extrasolar planet atmospheric models.Comment: Accepted to ApJ, 24 pages, 8 figure