arXiv subjects

Szilard Csizmadia

Publications and source records attributed to Szilard Csizmadia.

40 records · Page 3Linked to original sources

arXiv2016

K2-98 b: A 32-M$_\oplus$ Neptune-sized planet in a 10-day orbit transiting an F8 star

We report the discovery of K2-98 b (EPIC 211391664 b), a transiting Neptune-sized planet monitored by the K2 mission during its campaign 5. We combine the K2 time-series data with ground-based photometric and spectroscopic follow-up observations to confirm the planetary nature of the object and derive its mass, radius, and orbital parameters. K2-98 b is a warm Neptune-like planet in a 10-day orbit around a V=12.2~mag F-type star with $M_\star$=$ 1.074\pm0.042$, $R_\star$=$ 1.311 ^{+ 0.083} _{ - 0.048} $, and age of $5.2_{-1.0}^{+1.2}$~Gyr. We derive a planetary mass and radius of $M_\mathrm{p}$=$ 32.2 \pm 8.1 $ and $R_\mathrm{p}$=$4.3^{+0.3}_{-0.2}$. K2-98 b joins the relatively small group of Neptune-sized planets whose both mass and radius have been derived with a precision better than 25 %. We estimate that the planet will be engulfed by its host star in $\sim$3~Gyr, due to the evolution of the latter towards the red giant branch.

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arXiv2016

Two Hot Jupiters from K2 Campaign 4

We confirm the planetary nature of two transiting hot Jupiters discovered by the Kepler spacecraft's K2 extended mission in its Campaign 4, using precise radial velocity measurements from FIES@NOT, HARPS-N@TNG, and the coudé spectrograph on the McDonald Observatory 2.7 m telescope. K2-29 b (EPIC 211089792 b) transits a K1V star with a period of $3.2589263\pm0.0000015$ days; its orbit is slightly eccentric ($e=0.084_{-0.023}^{+0.032}$). It has a radius of $R_P=1.000_{-0.067}^{+0.071}$ $R_J$ and a mass of $M_P=0.613_{-0.026}^{+0.027}$ $M_J$. Its host star exhibits significant rotational variability, and we measure a rotation period of $P_{\mathrm{rot}}=10.777 \pm 0.031$ days. K2-30 b (EPIC 210957318 b) transits a G6V star with a period of $4.098503\pm0.000011$ days. It has a radius of $R_P=1.039_{-0.051}^{+0.050}$ $R_J$ and a mass of $M_P=0.579_{-0.027}^{+0.028}$ $M_J$. The star has a low metallicity for a hot Jupiter host, $[\mathrm{Fe}/\mathrm{H}]=-0.15 \pm 0.05$.

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arXiv2011

On the Mass of CoRoT-7b

The mass of CoRoT-7b, the first transiting superearth exoplanet, is still a subject of debate. A wide range of masses have been reported in the literature ranging from as high as 8 M_Earth to as low as 2.3 M_Earth. Although most mass determinations give a density consistent with a rocky planet, the lower value permits a bulk composition that can be up to 50% water. We present an analysis of the CoRoT-7b radial velocity measurements that uses very few and simple assumptions in treating the activity signal. By only analyzing those radial velocity data for which multiple measurements were made in a given night we remove the activity related radial velocity contribution without any a priori model. We demonstrate that the contribution of activity to the final radial velocity curve is negligible and that the K-amplitude due to the planet is well constrained. This yields a mass of 7.42 +/- 1.21 M_Earth and a mean density of rho = 10.4 +/- 1.8 gm cm^-3. CoRoT-7b is similar in mass and radius to the second rocky planet to be discovered, Kepler-10b, and within the errors they have identical bulk densities - they are virtual twins. These bulk densities lie close to the density - radius relationship for terrestrial planets similar to what is seen for Mercury. CoRoT-7b and Kepler-10b may have an internal structure more like Mercury than the Earth.

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arXiv2007

The Rapid Outbursting Star GM Cep: An EX-or in Tr 37?

We present optical, IR and millimeter observations of the solar-type star 13-277, also known as GM Cep, in the 4 Myr-old cluster Tr 37. GM Cep experiences rapid magnitude variations of more than 2 mag at optical wavelengths. We explore the causes of the variability, which seem to be dominated by strong increases in the accretion, being similar to EX-or episodes. The star shows high, variable accretion rates (up to ~10$^{-6}$ Msun/yr), signs of powerful winds, and it is a very fast rotator (Vsini~43 km/s). Its strong mid-IR excesses reveal a very flared disk and/or a remnant envelope, most likely out of hydrostatic equilibrium. The 1.3 millimeter fluxes suggest a relatively massive disk (Mdisk~0.1 Msun). Nevertheless, the millimeter mass is not enough to sustain increased accretion episodes over large timescales, unless the mass is underestimated due to significant grain growth. We finally explore the possibility of GM Cep having a binary companion, which could trigger disk instabilities producing the enhanced accretion episodes.

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