arXiv subjects

Abhinav Jindal

Publications and source records attributed to Abhinav Jindal.

3 recordsLinked to original sources

arXiv2020

Arid or Cloudy: Characterizing the Atmosphere of the super-Earth 55 Cancri e using High-Resolution Spectroscopy

The nearby super-Earth 55 Cnc e orbits a bright (V = 5.95 mag) star with a period of ~ 18 hours and a mass of ~ 8 Earth masses. Its atmosphere may be water-rich and have a large scale-height, though attempts to characterize it have yielded ambiguous results. Here we present a sensitive search for water and TiO in its atmosphere at high spectral resolution using the Gemini North telescope and the GRACES spectrograph. We combine observations with previous observations from Subaru and CFHT, improving the constraints on the presence of water vapor. We adopt parametric models with an updated planet radius based on recent measurements, and use a cross-correlation technique to maximize sensitivity. Our results are consistent with atmospheres that are cloudy or contain minimal amounts of water and TiO. Using these parametric models, we rule out a water-rich atmosphere (VMR >= 0.1%) with a mean molecular weight of <= 15 g/mol at a 3 sigma confidence level, improving on the previous limit by a significant margin. For TiO, we rule out a mean molecular weight of <= 5 g/mol with a 3 sigma confidence level for a VMR greater than 10^-8; for a VMR of greater than 10^-7, the limit rises to a mean molecular weight of <= 10 g/mol. We can rule out low mean-molecular-weight chemical equilibrium models both including and excluding TiO/VO at very high confidence levels (> 10 sigma). Overall, our results are consistent with an atmosphere with a high mean molecular weight and/or clouds, or no atmosphere.

astro-ph.EP↗

arXiv2019

The orbital anisotropy profiles of nearby globular clusters from Gaia Data Release 2

Gaia Data Release 2 provides a wealth of data to study the internal structure of nearby globular clusters. We use this data to investigate the internal kinematics of 11 nearby globular clusters, with a particular focus on their poorly-studied outer regions. We apply a strict set of selection criteria to remove contaminating sources and create pure cluster-member samples over a significant fraction of the radial range of each cluster. We confirm previous measurements of rotation (or a lack thereof) in the inner regions of several clusters, while extending the detection of rotation well beyond where it was previously measured and finding a steady decrease in rotation with radius. We also determine the orbital anisotropy profile and determine that clusters have isotropic cores, are radially anisotropic out to $\approx$ 4 half-light radii or $35\%$ of their limiting radii, and are then isotropic out to the limits of our datasets. We detect for the first time the presence of radial anisotropy in M 22, while confirming previous detections of radial anisotropy in 47 Tuc, M 3, M 13, M 15, and $ω$ Cen's innermost regions. The implications of these measurements are that clusters can be separated into two categories: 1) clusters with observed radial anisotropy that likely formed tidally under-filling or are dynamically young, and 2) clusters that are primarily isotropic that likely formed tidally filling or are dynamically old.

astro-ph.GA↗

arXiv2017

Galaxy-halo alignments in the Horizon-AGN cosmological hydrodynamical simulation

Intrinsic alignments of galaxies are a significant astrophysical systematic affecting cosmological constraints from weak gravitational lensing. Obtaining numerical predictions from hydrodynamical simulations of expected survey volumes is expensive, and a cheaper alternative relies on populating large dark matter-only simulations with accurate models of alignments calibrated on smaller hydrodynamical runs. This requires connecting the shapes and orientations of galaxies to those of dark matter haloes and to the large-scale structure. In this paper, we characterise galaxy-halo alignments in the Horizon-AGN cosmological hydrodynamical simulation. We compare the shapes and orientations of galaxies in the redshift range $0<z<3$ to those of their embedding dark matter haloes, and to the matching haloes of a twin dark-matter only run with identical initial conditions. We find that galaxy ellipticities in general cannot be predicted directly from halo ellipticities. The mean misalignment angle between the minor axis of a galaxy and its embedding halo is a function of halo mass, with residuals arising from the dependence of alignment on galaxy type, but not on environment. Haloes are much more strongly aligned among themselves than galaxies, and they decrease their alignment towards low redshift. Galaxy alignments compete with this effect, as galaxies tend to increase their alignment with haloes towards low redshift. We discuss the implications of these results for current halo models of intrinsic alignments and suggest several avenues for improvement.

astro-ph.CO↗