arXiv subjects

Stephanie Striegel

Publications and source records attributed to Stephanie Striegel.

22 records · Page 2Linked to original sources

arXiv2023

A Mini-Neptune Orbiting the Metal-poor K Dwarf BD+29 2654

We report the discovery and Doppler mass measurement of a 7.4-day 2.3-$R_\oplus$ mini-Neptune around a metal-poor K dwarf BD+29 2654 (TOI-2018). Based on a high-resolution Keck/HIRES spectrum, the Gaia parallax, and multi-wavelength photometry from the ultraviolet to the mid-infrared, we found that the host star has $T_{\text{eff}}=4174^{+34}_{-42}$ K, $\log{g}=4.62^{+0.02}_{-0.03}$, $[\text{Fe/H}]=-0.58\pm0.18$, $M_{\ast}=0.57\pm0.02~M_{\odot}$, and $R_{\ast}=0.62\pm0.01~R_{\odot}$. Precise Doppler measurements with Keck/HIRES revealed a planetary mass of $M_{\text{p}}=9.2\pm2.1~M_{\oplus}$ for TOI-2018 b. TOI-2018 b has a mass and radius that are consistent with an Earth-like core with a $\sim1\%$-by-mass hydrogen/helium envelope, or an ice-rock mixture. The mass of TOI-2018 b is close to the threshold for run-away accretion and hence giant planet formation. Such a threshold is predicted to be around 10$M_\oplus$ or lower for a low-metallicity (low-opacity) environment. If TOI-2018 b is a planetary core that failed to undergo run-away accretion, it may underline the reason why giant planets are rare around low-metallicity host stars (one possibility is their shorter disk lifetimes). With a K-band magnitude of 7.1, TOI-2018 b may be a suitable target for transmission spectroscopy with the James Webb Space Telescope. The system is also amenable to metastable Helium observation; the detection of a Helium exosphere would help distinguish between a H/He enveloped planet and a water world.

astro-ph.EP↗

arXiv2023

TOI-1994b: A Low Mass Eccentric Brown Dwarf Transiting A Subgiant Star

We present the discovery of TOI-1994b, a low-mass brown dwarf transiting a hot subgiant star on a moderately eccentric orbit. TOI-1994 has an effective temperature of $7700^{+720}_{-410}$ K, V magnitude of 10.51 mag and log(g) of $3.982^{+0.067}_{-0.065}$. The brown dwarf has a mass of $22.1^{+2.6}_{-2.5}$ $M_J$, a period of 4.034 days, an eccentricity of $0.341^{+0.054}_{-0.059}$, and a radius of $1.220^{+0.082}_{-0.071}$ $R_J$. TOI-1994b is more eccentric than other transiting brown dwarfs with similar masses and periods. The population of low mass brown dwarfs may have properties similar to planetary systems if they were formed in the same way, but the short orbital period and high eccentricity of TOI-1994b may contrast this theory. An evolved host provides a valuable opportunity to understand the influence stellar evolution has on the substellar companion's fundamental properties. With precise age, mass, and radius, the global analysis and characterization of TOI-1994b augments the small number of transiting brown dwarfs and allows the testing of substellar evolution models.

astro-ph.SR↗

arXiv2023

TOI-3235 b: a transiting giant planet around an M4 dwarf star

We present the discovery of TOI-3235 b, a short-period Jupiter orbiting an M-dwarf with a stellar mass close to the critical mass at which stars transition from partially to fully convective. TOI-3235 b was first identified as a candidate from TESS photometry, and confirmed with radial velocities from ESPRESSO, and ground-based photometry from HATSouth, MEarth-South, TRAPPIST-South, LCOGT, and ExTrA. We find that the planet has a mass of $\mathrm{0.665\pm0.025\,M_J}$ and a radius of $\mathrm{1.017\pm0.044\,R_J}$. It orbits close to its host star, with an orbital period of $\mathrm{2.5926\,d}$, but has an equilibrium temperature of $\mathrm{\approx 604 \, K}$, well below the expected threshold for radius inflation of hot Jupiters. The host star has a mass of $\mathrm{0.3939\pm0.0030\,M_\odot}$, a radius of $\mathrm{0.3697\pm0.0018\,R_\odot}$, an effective temperature of $\mathrm{3389 \, K}$, and a J-band magnitude of $\mathrm{11.706\pm0.025}$. Current planet formation models do not predict the existence of gas giants such as TOI-3235 b around such low-mass stars. With a high transmission spectroscopy metric, TOI-3235 b is one of the best-suited giants orbiting M-dwarfs for atmospheric characterization.

astro-ph.EP↗

arXiv2017

A Study of the Gamma-Ray Burst Fundamental Plane

Long gamma-ray bursts (GRBs) with a plateau phase in their X-ray afterglows obeys a three-dimensional (3D) relation (Dainotti et al. 2016), between the rest-frame time at the end of the plateau, Ta, its corresponding X-ray luminosity, La, and the peak luminosity in the prompt emission, Lpeak, an extension of the two-dimensional Dainotti relation. This 3D relation identifies a GRB fundamental plane whose existence we here confirm. We extend the original analysis with X-ray data untill July 2016 gathering 183 Swift GRBs with afterglow plateaus and known redshifts. We compare several GRB categories, such as shorts with extended emission, SEE, X-ray Flashes, GRBs associated with SNe, a sample of only long-duration GRBs (132), selected from the total sample by excluding GRBs of the previous categories, and the gold sample, composed by GRBs with light curves with good data coverage and relatively flat plateaus. The relation planes for each of these categories are not statistically different from the gold fundamental plane, with the exception of the SEE, which are hence identified as a physically distinct class of objects. The gold fundamental plane has an intrinsic scatter smaller than any plane derived from the other sample categories. Thus, the distance of any particular GRB category from this plane becomes a key parameter. Additionally, we tested this 3D relations by using GRBs observed at high energy, namely the peak luminosity values derived by the Fermi-Gamma Ray Burst Monitor (GBM). The 3D relation is also confirmed for GRBs observed by the GBM, thus showing its independence from the energy range. Furthermore, we computed the several category planes with T*a as a dependent parameter obtaining for each category smaller intrinsic scatters (reaching a reduction of $24\%$ for the long GRBs). The fundamental plane is independent from several prompt and afterglow parameters.

astro-ph.HE↗