arXiv subjects

Ravi kumar Kopparapu

Publications and source records attributed to Ravi kumar Kopparapu.

21 records · Page 2Linked to original sources

arXiv2009

Testing Binary Population Synthesis Models with Hot Subdwarfs

Models of binary star interactions have been successful in explaining the origin of field hot subdwarf (sdB) stars in short period systems, but longer-period systems that formed via Roche-lobe overflow (RLOF) mass transfer from the present sdB to its companion have received less attention. We map sets of initial binaries into present-day binaries that include sdBs and main-sequence stars, distinguishing "observable" sdBs from "hidden" ones. We aim to find out whether (1) the existing catalogues of sdBs are sufficiently fair samples of all the kinds of sdB binaries that theory predicts; or instead whether (2) large predicted hidden populations mandate the construction of new catalogues, perhaps using wide-field imaging surveys such as 2MASS, SDSS, and Galex. We also report on a pilot study to identify hidden subdwarfs, using 2MASS and GALEX data.

astro-ph.SR↗

arXiv2009

Population boundaries for compact white-dwarf binaries in LISA's amplitude-frequency domain

In an earlier investigation, we proposed population boundaries for both inspiralling and mass-transferring double white dwarf (DWD) systems in the distance independent "absolute" amplitude-frequency domain of the proposed space-based gravitational-wave (GW) detector, {\it LISA}. The degenerate zero temperature mass-radius (M-R) relationship of individual white dwarf stars that we assumed, in combination with the constraints imposed by Roche geometries, permits us to identify five key population boundaries for DWD systems in various phases of evolution. Here we use the non-zero entropy donor M-R relations of \cite{DB2003} to modify these boundaries for both DWD and neutron star-white dwarf (NSWD) binary systems. We find that the mass-transferring systems occupy a larger fraction of space in ``absolute'' amplitude-frequency domain compared to the simpler T=0 donor model. We also discuss how these boundaries are modified with the new evolutionary phases found by \cite{Deloyeetal2007}. In the initial contact phase, we find that the contact boundaries, which are the result of end of inspiral evolution, would have some width, as opposed to an abrupt cut-off described in our earlier T=0 model. This will cause an overlap between a DWDs $&$ NSWDs evolutionary trajectories, making them indistinguishable with only LISA observations within this region. In the cooling phase of the donor, which follows after the adiabatic donor evolution, the radius contracts, mass-transfer rate drops and slows down the orbital period evolution. Depending upon the entropy of the donor, these systems may then lie inside the fully degenerate T=0 boundaries, but LISA may be unable to detect these systems as they might be below the sensitivity limit or within the unresolved DWD background noise.

astro-ph↗

arXiv2009

Stability of additional planets in and around the habitable zone of the HD 47186 Planetary System

We study the dynamical stability of an additional, potentially habitable planet in the HD 47186 planetary system. Two planets are currently known in this system: a "hot Neptune" with a period of 4.08 days and a Saturn-mass planet with a period of 3.7 years. Here we consider the possibility that one or more undetected planets exist between the two known planets and possibly within the habitable zone in this system. Given the relatively low masses of the known planets, additional planets could have masses $\lsim 10 \mearth$, and hence be terrestrial-like and further improving potential habitability. We perform $N$-body simulations to identify the stable zone between planets $b$ and $c$ and find that much of the inner habitable zone can harbor a $10 \mearth$ planet. With the current radial-velocity threshold of $\sim 1$ m/s, an additional planet should be detectable if it lies at the inner edge of the habitable zone at 0.8 AU. We also show that the stable zone could contain two additional planets of $10 \mearth$ each if their eccentricities are lower than $\sim 0.3$.

astro-ph.EP↗