Abstract
In this paper, we consider the chain of resonances in the Kepler-80 system and evaluate the impact that the additional member of the resonant chain discovered by Shallue & Vanderburg has on ...the dynamics of the system and the physical parameters that can be recovered by a fit to the transit timing variations (TTVs). Ultimately, we calculate the mass of Kepler-80 g to be 0.8 ± 0.3
M
⊕
when assuming all planets have zero eccentricity, and 1.0 ± 0.3
M
⊕
when relaxing that assumption. We show that the outer five planets are in successive three-body mean-motion resonances (MMRs). We assess the current state of two-body MMRs in the system and find that the planets do not appear to be in two-body MMRs. We find that while the existence of the additional member of the resonant chain does not significantly alter the character of the Kepler-80 three-body MMRs, it can alter the physical parameters derived from the TTVs, suggesting caution should be applied when drawing conclusions from TTVs for potentially incomplete systems. We also compare our results to those of MacDonald et al., who perform a similar analysis on the same system with a different method. Although the results of this work and MacDonald et al. show that different fit methodologies and underlying assumptions can result in different measured orbital parameters, the most secure conclusion is that which holds true across all lines of analysis: Kepler-80 contains a chain of planets in three-body MMRs but not in two-body MMRs.
Minimum Orbital Periods of H-rich Bodies Rappaport, S.; Vanderburg, A.; Schwab, J. ...
The Astrophysical journal,
06/2021, Letnik:
913, Številka:
2
Journal Article
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Abstract
In this work we derive the minimum allowed orbital periods of H-rich bodies ranging in mass from Saturn’s mass to 1
M
⊙
, emphasizing gas giants and brown dwarfs (BDs) over the range ...0.0003–0.074
M
⊙
. Analytic fitting formulae for
as a function of the mass of the body and as a function of the mean density are presented. We assume that the density of the host star is sufficiently high so as not to limit the minimum period. In many instances this implies that the host star is a white dwarf. This work is aimed, in part, toward distinguishing BDs from planets that are found transiting the host white dwarf without recourse to near-infrared or radial velocity measurements. In particular, orbital periods of ≲100 minutes are very likely to be BDs. The overall minimum period over this entire mass range is ≃37 minutes.
ABSTRACT
We obtained high-resolution infrared spectroscopy and short-cadence photometry of the 600–800 Myr Praesepe star K2-100 during transits of its 1.67-d planet. This Neptune-size object, ...discovered by the NASA K2 mission, is an interloper in the ‘desert’ of planets with similar radii on short-period orbits. Our observations can be used to understand its origin and evolution by constraining the orbital eccentricity by transit fitting, measuring the spin-orbit obliquity by the Rossiter–McLaughlin effect, and detecting any extended, escaping the hydrogen–helium envelope with the 10 830 -Å line of neutral helium in the 2s3S triplet state. Transit photometry with 1-min cadence was obtained by the K2 satellite during Campaign 18 and transit spectra were obtained with the IRD spectrograph on the Subaru telescope. While the elevated activity of K2-100 prevented us from detecting the Rossiter–McLaughlin effect, the new photometry combined with revised stellar parameters allowed us to constrain the eccentricity to e < 0.15/0.28 with 90/99 per cent confidence. We modelled atmospheric escape as an isothermal, spherically symmetric Parker wind, with photochemistry driven by ultraviolet radiation, which we estimate by combining the observed spectrum of the active Sun with calibrations from observations of K2-100 and similar young stars in the nearby Hyades cluster. Our non-detection (<5.7 m Å) of a transit-associated He i line limits mass-loss of a solar-composition atmosphere through a T ≤ 10000 K wind to <0.3 M⊕ Gyr−1. Either K2-100b is an exceptional desert-dwelling planet, or its mass-loss is occurring at a lower rate over a longer interval, consistent with a core accretion-powered scenario for escape.
Aims.
A few well studied cataclysmic variables (CVs) have shown discrete characteristic frequencies of fast variability; the most prominent ones are around log(
f
/Hz) ≃ −3. Because we still have ...only small number statistics, we obtained a new observation to test whether this is a general characteristic of CVs, especially if mass transfer occurs at a high rate typical for dwarf nova in outbursts, in the so called high state.
Methods.
We analysed optical
Kepler
data of the quiescent nova and intermediate polar V4743 Sgr. This system hosts a white dwarf accreting through a disc in the high state. We calculated the power density spectra and searched for break or characteristic frequencies. Our goal is to assess whether the milihertz frequency of the flickering is a general characteristic.
Results.
V4743 Sgr has a clear break frequency at log(
f
/Hz) ≃ −3. This detection increases the probability that the megahertz characteristic frequency is a general feature of CVs in the high state, from 69% to 91%. Furthermore, we propose the possibility that the variability is generated by a similar mechanism as in the nova-like system MV Lyr, which would make V4743 Sgr unique.
Abstract
WD 1145+017 was observed from 2016 November through 2017 June for the purpose of further characterizing the transit behaviour of the dusty debris clouds orbiting this white dwarf. The ...optical observations were carried out with a small ground-based telescope run by an amateur astronomer, and covered 53 different nights over the 8-month interval. We have found that the optical activity has increased to the highest level observed since its discovery with Kepler K2, with approximately 17 per cent of the optical flux extinguished per orbit. The source exhibits some transits with depths of up to 55 per cent and durations as long as 2 h. The dominant period of the orbiting dust clouds during 2016–2017 is 4.49126 h. We present ‘waterfall’ images for the entire 2016–2017 and 2015–2016 observing seasons. In addition, the white dwarf was observed with the Chandra X-ray Observatory for 10-ks on each of four different occasions, separated by about a month each. The upper limit on the average X-ray flux from WD 1145+017 is ≃ 5 × 10−15 erg cm−2 s−1 (unabsorbed over the range 0.1–100 keV), which translates to an upper limit on the X-ray luminosity, Lx, of ≃ 2 × 1028 erg s−1. If $L_{\rm x} \simeq G M_{\rm wd} \dot{M}_{\rm acc}/R_{\rm wd}$, where Mwd and Rwd are the mass and radius of the white dwarf, and $\dot{M}_{\rm acc}$ is the accretion rate, then $\dot{M}_{\rm acc} \lesssim 2 \times 10^{11}$ g s−1. This is just consistent with the value of $\dot{M}$ that is inferred from the level of dust activity.
The single-sided pulsator CO Camelopardalis Kurtz, D W; Handler, G; Rappaport, S A ...
Monthly notices of the Royal Astronomical Society,
06/2020, Letnik:
494, Številka:
4
Journal Article
Recenzirano
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ABSTRACT
CO Cam (TIC 160268882) is the second ‘single-sided pulsator’ to be discovered. These are stars where one hemisphere pulsates with a significantly higher amplitude than the other side of the ...star. CO Cam is a binary star comprised of an Am δ Sct primary star with Teff = 7070 ± 150 K, and a spectroscopically undetected G main-sequence secondary star. The dominant pulsating side of the primary star is centred on the L1 point. We have modelled the spectral energy distribution combined with radial velocities, and independently the TESS light curve combined with radial velocities. Both of these give excellent agreement and robust system parameters for both stars. The δ Sct star is an oblique pulsator with at least four low radial overtone (probably) f modes with the pulsation axis coinciding with the tidal axis of the star, the line of apsides. Preliminary theoretical modelling indicates that the modes must produce much larger flux perturbations near the L1 point, although this is difficult to understand because the pulsating star does not come near to filling its Roche lobe. More detailed models of distorted pulsating stars should be developed. These newly discovered single-sided pulsators offer new opportunities for astrophysical inference from stars that are oblique pulsators in close binary stars.
Likely transiting exocomets detected by Kepler Rappaport, S; Vanderburg, A; Jacobs, T ...
Monthly notices of the Royal Astronomical Society,
2018-Feb-21, Letnik:
474, Številka:
2
Journal Article
Recenzirano
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Abstract
We present the first good evidence for exocomet transits of a host star in continuum light in data from the Kepler mission. The Kepler star in question, KIC 3542116, is of spectral type F2V ...and is quite bright at Kp = 10. The transits have a distinct asymmetric shape with a steeper ingress and slower egress that can be ascribed to objects with a trailing dust tail passing over the stellar disc. There are three deeper transits with depths of ≃ 0.1 per cent that last for about a day, and three that are several times more shallow and of shorter duration. The transits were found via an exhaustive visual search of the entire Kepler photometric data set, which we describe in some detail. We review the methods we use to validate the Kepler data showing the comet transits, and rule out instrumental artefacts as sources of the signals. We fit the transits with a simple dust-tail model, and find that a transverse comet speed of ∼35–50 km s−1 and a minimum amount of dust present in the tail of ∼1016 g are required to explain the larger transits. For a dust replenishment time of ∼10 d, and a comet lifetime of only ∼300 d, this implies a total cometary mass of ≳3 × 1017 g, or about the mass of Halley's comet. We also discuss the number of comets and orbital geometry that would be necessary to explain the six transits detected over the 4 yr of Kepler prime-field observations. Finally, we also report the discovery of a single comet-shaped transit in KIC 11084727 with very similar transit and host-star properties.
DS Tuc Ab is a Neptune-sized planet that orbits around a G star in the 45 Myr old Tucana-Horologium moving group. Here, we report the measurement of the sky-projected angle between the stellar spin ...axis and the planet's orbital axis, based on the observation of the Rossiter-McLaughlin effect during three separate planetary transits. The orbit appears to be well aligned with the equator of the host star, with a projected obliquity of . In addition to the distortions in the stellar absorption lines due to the transiting planet, we observed variations that we attribute to large starspots, with angular sizes of tens of degrees. The technique that we have developed for simultaneous modeling of starspots and the planet-induced distortions may be useful in other observations of planets around active stars.
Drifting asteroid fragments around WD 1145+017 Rappaport, S; Gary, B. L; Kaye, T ...
Monthly notices of the Royal Astronomical Society,
06/2016, Letnik:
458, Številka:
4
Journal Article
Recenzirano
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We have obtained extensive photometric observations of the polluted white dwarf WD 1145+017 which has been reported to be transited by at least one, and perhaps several, large asteroids with dust ...emission. Observation sessions on 37 nights spanning 2015 November to 2016 January with small to modest size telescopes have detected 237 significant dips in flux. Periodograms reveal a significant periodicity of 4.5004 h consistent with the dominant (‘A’) period detected with K2. The folded light curve shows an hour-long depression in flux with a mean depth of nearly 10 per cent. This depression is, in turn, comprised of a series of shorter and sometimes deeper dips which would be unresolvable with K2. We also find numerous dips in flux at other orbital phases. Nearly all of the dips associated with this activity appear to drift systematically in phase with respect to the ‘A’ period by about 2.5 min d−1 with a dispersion of ∼0.5 min d−1, corresponding to a mean drift period of 4.4928 h. We are able to track ∼15 discrete drifting features. The ‘B’–‘F’ periods found with K2 are not detected, but we would not necessarily have expected to see them. We explain the drifting motion as due to smaller fragmented bodies that break off from the asteroid and go into a slightly smaller orbit. In this interpretation, we can use the drift rate to determine the mass of the asteroid, which we find to be ≈1023 g, or about 1/10th the mass of Ceres.
Ultra-short period (USP) planets are a class of exoplanets with periods shorter than one day. The origin of this sub-population of planets is still unclear, with different formation scenarios highly ...dependent on the composition of the USP planets. A better understanding of this class of exoplanets will, therefore, require an increase in the sample of such planets that have accurate and precise masses and radii, which also includes estimates of the level of irradiation and information about possible companions. Here we report a detailed characterization of a USP planet around the solar-type star HD 80653 ≡EP 251279430 using the K2 light curve and 108 precise radial velocities obtained with the HARPS-N spectrograph, installed on the Telescopio Nazionale
Galileo
. From the K2 C16 data, we found one super-Earth planet (
R
b
= 1.613 ± 0.071
R
⊕
) transiting the star on a short-period orbit (
P
b
= 0.719573 ± 0.000021 d). From our radial velocity measurements, we constrained the mass of HD 80653 b to
M
b
= 5.60 ± 0.43
M
⊕
. We also detected a clear long-term trend in the radial velocity data. We derived the fundamental stellar parameters and determined a radius of
R
⋆
= 1.22 ± 0.01
R
⊙
and mass of
M
⋆
= 1.18 ± 0.04
M
⊙
, suggesting that HD 80653 has an age of 2.7 ± 1.2 Gyr. The bulk density (
ρ
b
= 7.4 ± 1.1 g cm
−3
) of the planet is consistent with an Earth-like composition of rock and iron with no thick atmosphere. Our analysis of the K2 photometry also suggests hints of a shallow secondary eclipse with a depth of 8.1 ± 3.7 ppm. Flux variations along the orbital phase are consistent with zero. The most important contribution might come from the day-side thermal emission from the surface of the planet at
T
~ 3480 K.
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