Spectroscopic Survey of {\gamma} Doradus Stars I. Comprehensive atmospheric parameters and abundance analysis of {\gamma} Doradus stars

We present a spectroscopic survey of known and candidate $\gamma$\,Doradus stars. The high-resolution, high signal-to-noise spectra of 52 objects were collected by five different spectrographs. The spectral classification, atmospheric parameters (\teff, $\log g$, $\xi$), $v\sin i$ and chemical composition of the stars were derived. The stellar spectral and luminosity classes were found between G0-A7 and IV-V, respectively. The initial values for \teff\ and \logg\ were determined from the photometric indices and spectral energy distribution. Those parameters were improved by the analysis of hydrogen lines. The final values of \teff, \logg\ and $\xi$ were derived from the iron lines analysis. The \teff\ values were found between 6000\,K and 7900\,K, while \logg\,values range from 3.8 to 4.5\,dex. Chemical abundances and $v\sin i$ values were derived by the spectrum synthesis method. The $v\sin i$ values were found between 5 and 240\,km\,s$^{-1}$. The chemical abundance pattern of $\gamma$\,Doradus stars were compared with the pattern of non-pulsating stars. It turned out that there is no significant difference in abundance patterns between these two groups. Additionally, the relations between the atmospheric parameters and the pulsation quantities were checked. A strong correlation between the $v\sin i$ and the pulsation periods of $\gamma$\,Doradus variables was obtained. The accurate positions of the analysed stars in the H-R diagram have been shown. Most of our objects are located inside or close to the blue edge of the theoretical instability strip of $\gamma$\,Doradus.Comment: 18 pages, 13 figure

Spectroscopic Pulsational Frequency Identification and Mode Determination of Gamma Doradus Star HD135825

We present the mode identification of frequencies found in spectroscopic observations of the Gamma Doradus star HD135825. Four frequencies were successfully identified: 1.3150 +/- 0.0003 1/d; 0.2902 +/- 0.0004 1/d; 1.4045 +/- 0.0005 1/d; and 1.8829 +/- 0.0005 1/d. These correspond to (l, m) modes of (1,1), (2,-2), (4,0) and (1,1) respectively. Additional frequencies were found but they were below the signal-to-noise limit of the Fourier spectrum and not suitable for mode identification. The rotational axis inclination and vsini of the star were determined to be 87 degrees (nearly edge-on) and 39.7 km/s (moderate for Gamma Doradus stars) respectively. A simultaneous fit of these four modes to the line profile variations in the data gives a reduced chi square of 12.7. We confirm, based on the frequencies found, that HD135825 is a bona fide Gamma Doradus star.Comment: Accepted to MNRAS 2012 March

The Mt John University Observatory Search For Earth-mass Planets In The Habitable Zone Of Alpha Centauri

The "holy grail" in planet hunting is the detection of an Earth-analog: a planet with similar mass as the Earth and an orbit inside the habitable zone. If we can find such an Earth-analog around one of the stars in the immediate solar neighborhood, we could potentially even study it in such great detail to address the question of its potential habitability. Several groups have focused their planet detection efforts on the nearest stars. Our team is currently performing an intensive observing campaign on the alpha Centauri system using the Hercules spectrograph at the 1-m McLellan telescope at Mt John University Observatory (MJUO) in New Zealand. The goal of our project is to obtain such a large number of radial velocity measurements with sufficiently high temporal sampling to become sensitive to signals of Earth-mass planets in the habitable zones of the two stars in this binary system. Over the past years, we have collected more than 45,000 spectra for both stars combined. These data are currently processed by an advanced version of our radial velocity reduction pipeline, which eliminates the effect of spectral cross-contamination. Here we present simulations of the expected detection sensitivity to low-mass planets in the habitable zone by the Hercules program for various noise levels. We also discuss our expected sensitivity to the purported Earth-mass planet in an 3.24-d orbit announced by Dumusque et al.~(2012).Comment: 16 pages, 7 figures, accepted for publication in the International Journal of Astrobiolog

MOA 2003-BLG-37: A Bulge Jerk-Parallax Microlens Degeneracy

We analyze the Galactic bulge microlensing event MOA-2003-BLG-37. Although the Einstein timescale is relatively short, t_e=43 days, the lightcurve displays deviations consistent with parallax effects due to the Earth's accelerated motion. We show that the chi^2 surface has four distinct local minima that are induced by the ``jerk-parallax'' degeneracy, with pairs of solutions having projected Einstein radii, \tilde r_e = 1.76 AU and 1.28 AU, respectively. This is the second event displaying such a degeneracy and the first toward the Galactic bulge. For both events, the jerk-parallax formalism accurately describes the offsets between the different solutions, giving hope that when extra solutions exist in future events, they can easily be found. However, the morphologies of the chi^2 surfaces for the two events are quite different, implying that much remains to be understood about this degeneracy.Comment: 19 pages, 3 figures, 1 table, ApJ, in press, 1 July 200

Microlensing optical depth towards the Galactic bulge from MOA observations during 2000 with Difference Image Analysis

We analyze the data of the gravitational microlensing survey carried out by by the MOA group during 2000 towards the Galactic Bulge (GB). Our observations are designed to detect efficiently high magnification events with faint source stars and short timescale events, by increasing the the sampling rate up to 6 times per night and using Difference Image Analysis (DIA). We detect 28 microlensing candidates in 12 GB fields corresponding to 16 deg^2. We use Monte Carlo simulations to estimate our microlensing event detection efficiency, where we construct the I-band extinction map of our GB fields in order to find dereddened magnitudes. We find a systematic bias and large uncertainty in the measured value of the timescale $t_{\rm Eout}$ in our simulations. They are associated with blending and unresolved sources, and are allowed for in our measurements. We compute an optical depth tau = 2.59_{-0.64}^{+0.84} \times 10^{-6} towards the GB for events with timescales 0.3<t_E<200 days. We consider disk-disk lensing, and obtain an optical depth tau_{bulge} = 3.36_{-0.81}^{+1.11} \times 10^{-6}[0.77/(1-f_{disk})] for the bulge component assuming a 23% stellar contribution from disk stars. These observed optical depths are consistent with previous measurements by the MACHO and OGLE groups, and still higher than those predicted by existing Galactic models. We present the timescale distribution of the observed events, and find there are no significant short events of a few days, in spite of our high detection efficiency for short timescale events down to t_E = 0.3 days. We find that half of all our detected events have high magnification (>10). These events are useful for studies of extra-solar planets.Comment: 65 pages and 30 figures, accepted for publication in ApJ. A systematic bias and uncertainty in the optical depth measurement has been quantified by simulation

Improving the Prospects for Detecting Extrasolar Planets in Gravitational Microlensing in 2002

Gravitational microlensing events of high magnification have been shown to be promising targets for detecting extrasolar planets. However, only a few events of high magnification have been found using conventional survey techniques. Here we demonstrate that high magnification events can be readily found in microlensing surveys using a strategy that combines high frequency sampling of target fields with online difference imaging analysis. We present 10 microlensing events with peak magnifications greater than 40 that were detected in real-time towards the Galactic Bulge during 2001 by MOA. We show that Earth mass planets can be detected in future events such as these through intensive follow-up observations around the event peaks. We report this result with urgency as a similar number of such events are expected in 2002.Comment: 11 pages, 3 embedded ps figures including 2 colour, revised version accepted by MNRA