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We present a new method of analysing and quantifying velocity structure in star forming regions suitable for the rapidly increasing quantity and quality of stellar position-velocity data. The method can be applied to data in any number of dimensions, does not require the centre or characteristic size (e.g. radius) of the region to be determined, and can be applied to regions with any underlying density and velocity structure. We test the method on a variety of example datasets and show it is robust with realistic observational uncertainties and selection effects. This method identifies velocity structures/scales in a region, and allows a direct comparison to be made between regions.
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Pulsar nulling is a phenomenon of sudden cessation of pulse emission for a number of periods. The nulling fraction was often used to characterize the phenomenon. We propose a new method to analyse pulsar nulling phenomenon, by involving two key parameters, the nulling degree, $chi$, which is defined as the angle in a rectangular coordinates for the numbers of nulling periods and bursting periods, and the nulling scale, $ N $, which is defined as the effective length of the consecutive nulling periods and bursting periods. The nulling degree $chi$ can be calculated by $tan chi = N_{rm nulling} / N_{rm bursting} $ and the mean is related to the nulling fraction, while the nulling scale, $ N $, is also a newly defined fundamental parameter which indicates how often the nulling occurs. We determined the distributions of $chi$ and $ N $ for 10 pulsars by using the data in literature. We found that the nulling degree $chi$ indicates the relative length of nulling to that of bursting, and the nulling scale $ N $ is found to be related to the derivative of rotation frequency and hence the loss rate of rotational energy of pulsars. Their deviations reflect the randomness of the nulling process.
High-Resolution Spectroscopy (HRS) has been used to study the composition and dynamics of exoplanetary atmospheres. In particular, the spectrometer CRIRES installed on the ESO-VLT has been used to record high-resolution spectra in the Near-IR of gaseous exoplanets. Here we present a new automatic pipeline to analyze CRIRES data-sets. Said pipeline is based on a novel use of Principal Component Analysis (PCA) and Cross-Correlation Function (CCF). The exoplanetary atmosphere is modeled with the $tau$-REx code using opacities at high temperature from the ExoMol project. In this work, we tested our analysis tools on the detection of CO and H$_2$O in the atmospheres of the hot-Jupiters HD209458b and HD189733b. The results of our pipeline are in agreement with previous results in the literature and other techniques.
We present a new catalogue of 18 080 radial velocity standard stars selected from the APOGEE data. These RV standard stars are observed at least three times and have a median stability ($3sigma_{rm RV}$) around 240 m s$^{-1}$ over a time baseline longer than 200 days. They are largely distributed in the northern sky and could be extended to the southern sky by the future APOGEE-2 survey. Most of the stars are red giants ($J - K_{rm s} ge 0.5$) owing to the APOGEE target selection criteria. Only about ten per cent of them are main-sequence stars. The $H$ band magnitude range of the stars is 7-12.5 mag with the faint limit much fainter than the magnitudes of previous RV standard stars. As an application, we show the new set of standard stars to determine the radial velocity zero points of the RAVE, the LAMOST {and the Gaia-RVS} Galactic spectroscopic surveys.
The gravitational redshift induced by stellar surface gravity is notoriously difficult to measure for non-degenerate stars, since its amplitude is small in comparison with the typical Doppler shift induced by stellar radial velocity. In this study, we make use of the large observational data set of the Gaia mission to achieve a significant reduction of noise caused by these random stellar motions. By measuring the differences in velocities between the components of pairs of co-moving stars and wide binaries, we are able to statistically measure gravitational redshift and nullify the effect of the peculiar motions of the stars. For the subset of stars considered in this study, we find a positive correlation between the observed differences in Gaia radial velocities and the differences in surface gravity inferred from effective temperature and luminosity measurements. This corresponds to the first ever measurement of extra-Solar surface gravity induced gravitational redshift in non-degenerate stars. Additionally, we study the sub-dominant effects of convective blueshifting of emission lines, effects of binary motion, and possible systematic errors in radial velocity measurements within Gaia. Results from the technique presented in this study are expected to improve significantly with data from the next Gaia data release. Such improvements could be used to constrain the mass-luminosity relation and stellar models which predict the magnitude of convective blueshift.
The analysis of the CoRoT space mission data was performed aiming to test a method that selects, among the several light curves observed, the transiting systems that likely host a low-mass star orbiting the main target. The method identifies stellar companions by fitting a model to the observed transits. Applying this model, that uses equations like Keplers third law and an empirical mass-radius relation, it is possible to estimate the mass and radius of the primary and secondary objects as well as the semimajor axis and inclination angle of the orbit. We focus on how the method can be used in the characterisation of transiting systems having a low-mass stellar companion with no need to be monitored with radial-velocity measurements or ground-based photometric observations. The model, which provides a good estimate of the system parameters, is also useful as a complementary approach to select possible planetary candidates. A list of confirmed binaries together with our estimate of their parameters are presented. The characterisation of the first twelve detected CoRoT exoplanetary systems was also performed and agrees very well with the results of their respective announcement papers. The comparison with confirmed systems validates our method, specially when the radius of the secondary companion is smaller than 1.5 Rjup, in the case of planets, or larger than 2 Rjup, in the case of low-mass stars. Intermediate situations are not conclusive.
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