85 research outputs found
Dynamical Measurements of the Interior Structure of Exoplanets
Giant gaseous planets often reside on orbits in sufficient proximity to their
host stars for the planetary quadrupole gravitational field to become
non-negligible. In presence of an additional planetary companion, a precise
characterization of the system's orbital state can yield meaningful constraints
on the transiting planet's interior structure. However, such methods can
require a very specific type of system. This paper explores the dynamic range
of applicability of these methods and shows that interior structure
calculations are possible for a wide array of orbital architectures. The
HAT-P-13 system is used as a case study, and the implications of perturbations
arising from a third distant companion on the feasibility of an interior
calculation are discussed. We find that the method discussed here is likely to
be useful in studying other planetary systems, allowing the possibility of an
expanded survey of the interiors of exoplanets.Comment: Accepted to Ap
The Planet Nine Hypothesis
Over the course of the past two decades, observational surveys have unveiled
the intricate orbital structure of the Kuiper Belt, a field of icy bodies
orbiting the Sun beyond Neptune. In addition to a host of readily-predictable
orbital behavior, the emerging census of trans-Neptunian objects displays
dynamical phenomena that cannot be accounted for by interactions with the known
eight-planet solar system alone. Specifically, explanations for the observed
physical clustering of orbits with semi-major axes in excess of AU,
the detachment of perihelia of select Kuiper belt objects from Neptune, as well
as the dynamical origin of highly inclined/retrograde long-period orbits remain
elusive within the context of the classical view of the solar system. This
newly outlined dynamical architecture of the distant solar system points to the
existence of a new planet with mass of , residing on
a moderately inclined orbit () with semi-major axis AU and eccentricity between . This paper
reviews the observational motivation, dynamical constraints, and prospects for
detection of this proposed object known as Planet Nine.Comment: 92 pages, 28 figures, published in Physics Report
Extracting Radial Velocities of A- and B-type Stars from Echelle Spectrograph Calibration Spectra
We present a technique to extract radial velocity measurements from echelle
spectrograph observations of rapidly rotating stars ( km
s). This type of measurement is difficult because the line widths of
such stars are often comparable to the width of a single echelle order. To
compensate for the scarcity of lines and Doppler information content, we have
developed a process that forward-models the observations, fitting the radial
velocity shift of the star for all echelle orders simultaneously with the
echelle blaze function. We use our technique to extract radial velocity
measurements from a sample of rapidly rotating A- and B-type stars used as
calibrator stars observed by the California Planet Survey observations. We
measure absolute radial velocities with a precision ranging from 0.5-2.0 km
s per epoch for more than 100 A- and B-type stars. In our sample of 10
well-sampled stars with radial velocity scatter in excess of their measurement
uncertainties, three of these are single-lined binaries with long observational
baselines. From this subsample, we present detections of two previously unknown
spectroscopic binaries and one known astrometric system. Our technique will be
useful in measuring or placing upper limits on the masses of sub-stellar
companions discovered by wide-field transit surveys, and conducting future
spectroscopic binarity surveys and Galactic space-motion studies of massive
and/or young, rapidly-rotating stars.Comment: Accepted to ApJ
The Origin of Universality in the Inner Edges of Planetary Systems
The characteristic orbital period of the inner-most objects within the
galactic census of planetary and satellite systems appears to be nearly
universal, with on the order of a few days. This paper presents a
theoretical framework that provides a simple explanation for this phenomenon.
By considering the interplay between disk accretion, magnetic field generation
by convective dynamos, and Kelvin-Helmholtz contraction, we derive an
expression for the magnetospheric truncation radius in astrophysical disks, and
find that the corresponding orbital frequency is independent of the mass of the
host body. Our analysis demonstrates that this characteristic frequency
corresponds to a period of days, although intrinsic variations in
system parameters are expected to introduce a factor of spread in
this result. Standard theory of orbital migration further suggests that planets
should stabilize at an orbital period that exceeds disk truncation by a small
margin. Cumulatively, our findings predict that the periods of close-in bodies
should span days - a range that is consistent with observations.Comment: 9 pages, 4 figures, accepted to ApJ
Detection of Diatomic Carbon in 2I/Borisov
2I/Borisov is the first-ever observed interstellar comet (and the second detected interstellar object (ISO)). It was discovered on 2019 August 30 and has a heliocentric orbital eccentricity of ~3.35, corresponding to a hyperbolic orbit that is unbound to the Sun. Given that it is an ISO, it is of interest to compare its properties—such as composition and activity—with the comets in our solar system. This study reports low-resolution optical spectra of 2I/Borisov. The spectra were obtained by the MDM Observatory Hiltner 2.4 m telescope/Ohio State Multi-Object Spectrograph (on 2019 October 31.5 and November 4.5, UT). The wavelength coverage spanned from 3700 to 9200 Å. The dust continuum reflectance spectra of 2I/Borisov show that the spectral slope is steeper in the blue end of the spectrum (compared to the red). The spectra of 2I/Borisov clearly show CN emission at 3880 Å, as well as C2 emission at both 4750 and 5150 Å. Using a Haser model to covert the observed fluxes into estimates for the molecular production rates, we find Q(CN) = 2.4 ± 0.2 × 10²⁴ s⁻¹, and Q(C₂) = (5.5 ± 0.4) × 10²³ s⁻¹ at the heliocentric distance of 2.145 au. Our Q(CN) estimate is consistent with contemporaneous observations, and the Q(C₂) estimate is generally below the upper limits of previous studies. We derived the ratio Q(C₂)/Q(CN) = 0.2 ± 0.1, which indicates that 2I/Borisov is depleted in carbon-chain species, but is not empty. This feature is not rare for the comets in our solar system, especially in the class of Jupiter-family comets
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