Abstract
We acquired high-resolution infrared spectra of CI Tau, the host star of one of the few young planet candidates amenable to direct spectroscopic detection. We confirm the planet’s existence ...with a direct detection of CO in the planet’s atmosphere. We also calculate a mass of 11.6
M
J
based on the amplitude of its radial velocity variations. We estimate its flux contrast with its host star to get an absolute magnitude estimate for the planet of 8.17 in the
K-
band. This magnitude implies the planet formed via a “hot start” formation mechanism. This makes CI Tau b the youngest confirmed exoplanet as well as the first exoplanet around a T Tauri star with a directly determined, model-independent dynamical mass.
Abstract
Magnetic star–planet interactions (SPI) provide a detection method and
insight into exoplanet magnetic fields and, in turn, exoplanet interiors and
atmospheric environments. These signatures ...can be sporadic and difficult to
confirm for single-epoch observations of a system due to inhomogeneous stellar
magnetospheres and periodic variability in stellar magnetism. Thus, an ideal SPI
search consists of multiple epochs containing observations on consecutive nights
spanning at least one complete planetary orbit. Such data sets are rare but do
exist for some of the most intensely studied hot Jupiter systems. One such
system is HD 189733 for which six suitable SPI data sets exist, the result of
spectroscopic monitoring to perform some of the first SPI searches and also to
study the star’s magnetic field. Here we perform a uniform analysis of six
archival Ca
ii
K data sets for HD 189733, spanning 2006 June through
2015 July, in order to search for magnetic SPI signatures in the chromospheric
line variations. We find significant evidence for modulations of Ca
ii
K with a 2.29 ± 0.04 day period in the 2013 August data,
which is consistent with the planet’s orbital period. The peak in the
orbital variations occurs at
ϕ
orb
≈ 0.9, which corresponds
to the SPI emission leading the planet with a phase difference of
Δ
ϕ
≈ 40° from the
sub-planetary point. This is consistent with the phase-lead predictions of
nonlinear force-free magnetic field SPI models. The stellar magnetic field
strength at the planet’s orbit was greatest in 2013 August, which, due to
the energy released in magnetic SPI scaling with
B
*
, lends strength to the SPI
interpretation.
Abstract
Measured spectral shifts due to intrinsic stellar variability (e.g., pulsations, granulation) and activity (e.g., spots, plages) are the largest source of error for extreme-precision ...radial-velocity (EPRV) exoplanet detection. Several methods are designed to disentangle stellar signals from true center-of-mass shifts due to planets. The Extreme-precision Spectrograph (EXPRES) Stellar Signals Project (ESSP) presents a self-consistent comparison of 22 different methods tested on the same extreme-precision spectroscopic data from EXPRES. Methods derived new activity indicators, constructed models for mapping an indicator to the needed radial-velocity (RV) correction, or separated out shape- and shift-driven RV components. Since no ground truth is known when using real data, relative method performance is assessed using the total and nightly scatter of returned RVs and agreement between the results of different methods. Nearly all submitted methods return a lower RV rms than classic linear decorrelation, but no method is yet consistently reducing the RV rms to sub-meter-per-second levels. There is a concerning lack of agreement between the RVs returned by different methods. These results suggest that continued progress in this field necessitates increased interpretability of methods, high-cadence data to capture stellar signals at all timescales, and continued tests like the ESSP using consistent data sets with more advanced metrics for method performance. Future comparisons should make use of various well-characterized data sets—such as solar data or data with known injected planetary and/or stellar signals—to better understand method performance and whether planetary signals are preserved.
Variability of Classical T Tauri stars (CTTS) occurs over a vast range of timescales. CTTS in particular are subject to variability caused by accretion shocks, which can occur stochastically, ...periodically, or quasi-periodically on timescales over a few days. The detectability of young planets within these systems is likely hampered by activity; therefore, it is essential that we understand the origin of young star variability over a range of timescales to help disentangle stellar activity from signatures of planetary origin. We present an analysis of the stochastic small-amplitude photometric variability in the K2 lightcurve of CI Tau occurring on timescales of 1 day. We find the amplitude of this variability exhibits the same periodic signatures as detected in the large-amplitude variability, indicating that the physical mechanism modulating these brightness features is the same. The periods detected are also in agreement with the rotation period of the star (∼6.6 days) and the orbital period of the planet (∼9.0 days) known to drive pulsed accretion onto the star.
Abstract
We present fundamental parameters for 110 canonical
K
- and
M
-type (1.3−0.13
M
⊙
) Taurus-Auriga young stellar objects (YSOs). The analysis produces a simultaneous determination of ...effective temperature (
T
eff
), surface gravity (log
g
), magnetic-field strength (B), and projected rotational velocity (
v
sin
i
). Our method employed synthetic spectra and high-resolution (
R
∼ 45,000) near-infrared spectra taken with the Immersion GRating INfrared Spectrometer (IGRINS) to fit specific
K
-band spectral regions most sensitive to those parameters. The use of these high-resolution spectra reduces the influence of distance uncertainties, reddening, and non-photospheric continuum emission on the parameter determinations. The median total (fit + systematic) uncertainties were 170 K, 0.28 dex, 0.60 kG, 2.5 km s
−1
for
T
eff
, log
g
, B, and
v
sin
i
, respectively. We determined B for 41 Taurus YSOs (upper limits for the remainder) and find systematic offsets (lower
T
eff
, higher log
g
and
v
sin
i
) in parameters when B is measurable but not considered in the fit. The average log
g
for the Class
ii
and Class
iii
objects differs by 0.23 ± 0.05 dex, which is consistent with Class
iii
objects being the more evolved members of the star-forming region. However, the dispersion in log
g
is greater than the uncertainties, which highlights how the YSO classification correlates with age (log
g
), yet there are exceptionally young (lower log
g
) Class
iii
YSOs and relatively old (higher log
g
) Class
ii
YSOs with unexplained evolutionary histories. The spectra from this work are provided in an online repository along with TW Hydrae Association comparison objects and the model grid used in our analysis.
Abstract
Coronal mass ejections (CMEs) are a prominent contributor to solar system space weather and might have impacted the Sun’s early angular momentum evolution. A signal diagnostic of CMEs on the ...Sun is coronal dimming: a drop in coronal emission, tied to the mass of the CME, that is the direct result of removing emitting plasma from the corona. We present the results of a coronal dimming analysis of Fe
xii
1349 Å and Fe
xxi
1354 Å emission from
ϵ
Eridani (
ϵ
Eri), a young K2 dwarf, with archival far-ultraviolet observations by the Hubble Space Telescope’s Cosmic Origins Spectrograph. Following a flare in 2015 February,
ϵ
Eri’s Fe
xxi
emission declined by 81 ± 5%. Although enticing, a scant 3.8 minutes of preflare observations allows for the possibility that the Fe
xxi
decline was the decay of an earlier, unseen flare. Dimming nondetections following each of three prominent flares constrain the possible mass of ejected Fe
xii
-emitting (1 MK) plasma to less than a few × 10
15
g. This implies that CMEs ejecting this much or more 1 MK plasma occur less than a few times per day on
ϵ
Eri. On the Sun, 10
15
g CMEs occur once every few days. For
ϵ
Eri, the mass-loss rate due to CME-ejected 1 MK plasma could be < 0.6
M
̇
⊙
, well below the star’s estimated 30
M
̇
⊙
mass-loss rate (wind + CMEs). The order-of-magnitude formalism we developed for these mass estimates can be broadly applied to coronal dimming observations of any star.
Abstract
We present spectroscopic measurements of the Rossiter–McLaughlin effect for WASP-148b, the only known hot Jupiter with a nearby warm-Jupiter companion, from the WIYN/NEID and Keck/HIRES ...instruments. This is one of the first scientific results reported from the newly commissioned NEID spectrograph, as well as the second obliquity constraint for a hot Jupiter system with a close-in companion, after WASP-47. WASP-148b is consistent with being in alignment with the sky-projected spin axis of the host star, with
λ
=
−
8
.°
2
−
9
.°
7
+
8
.°
7
. The low obliquity observed in the WASP-148 system is consistent with the orderly-alignment configuration of most compact multi-planet systems around cool stars with obliquity constraints, including our solar system, and may point to an early history for these well-organized systems in which migration and accretion occurred in isolation, with relatively little disturbance. By contrast, previous results have indicated that high-mass and hot stars appear to more commonly host a wide range of misaligned planets: not only single hot Jupiters, but also compact systems with multiple super-Earths. We suggest that, to account for the high rate of spin–orbit misalignments in both compact multi-planet and isolated-hot-Jupiter systems orbiting high-mass and hot stars, spin–orbit misalignments may be caused by distant giant planet perturbers, which are most common around these stellar types.
Coronal mass ejections (CMEs) are a prominent contributor to solar system space weather and might have impacted the Sun's early angular momentum evolution. A signal diagnostic of CMEs on the Sun is ...coronal dimming: a drop in coronal emission, tied to the mass of the CME, that is the direct result of removing emitting plasma from the corona. We present the results of a coronal dimming analysis of Fe XII 1349 Å and Fe XXI 1354 Å emission from ϵ Eridani ( ϵ Eri), a young K2 dwarf, with archival far-ultraviolet observations by the Hubble Space Telescope's Cosmic Origins Spectrograph. Following a flare in 2015 February, ϵ Eri's Fe XXI emission declined by 81 ± 5%. Although enticing, a scant 3.8 minutes of preflare observations allows for the possibility that the Fe XXI decline was the decay of an earlier, unseen flare. Dimming nondetections following each of three prominent flares constrain the possible mass of ejected Fe XII-emitting (1 MK) plasma to less than a few × 1015 g. This implies that CMEs ejecting this much or more 1 MK plasma occur less than a few times per day on ϵ Eri. On the Sun, 1015 g CMEs occur once every few days. For Eri, the mass-loss rate due to CME-ejected 1 MK plasma could be < 0.6 ṀꙨ well below the star's estimated 30 ṀꙨ mass-loss rate (wind + CMEs). The order-of-magnitude formalism we developed for these mass estimates can be broadly applied to coronal dimming observations of any star.
ABSTRACT
We present the results of a multiwavelength Professional–Amateur campaign to study the behaviour of flares from the active M1.5V star binary CR Draconis. CR Dra was observed with Transiting ...Exoplanet Survey Satellite (TESS) 20-s photometry, Swift near-ultraviolet (NUV) grism spectroscopy and with ground-based optical photometry and spectroscopy from a global collaboration of amateur astronomers. We detected 14 flares with TESS and Swift simultaneously, one of which also had simultaneous ground-based photometry and spectroscopy. We used the simultaneous two-colour optical and NUV observations to characterize the temperature evolution of the flare and test the accuracy of using optical data to predict NUV emission. We measured a peak temperature of $7100^{+150}_{-130}$ K for this flare, cooler than the typically assumed 9000 K blackbody model used by flare studies. We also found that the 9000 K blackbody overestimated the NUV flux for other flares in our sample, which we attributed to our Swift observations occurring during flare decays, highlighting the phase-dependence for the accuracy of flare models.
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