While brown dwarfs show similarities to stars early in their lives, their spin evolutions are much more akin to those of planets. We have used light curves from the K2 mission to measure new rotation ...periods for 18 young brown dwarfs in the Taurus star-forming region. Our sample spans masses from 0.02 to 0.08 M and has been characterized extensively in the past. To search for periods, we utilize three different methods (autocorrelation, periodogram, Gaussian processes). The median period for brown dwarfs with disks is twice as long as for those without (3.1 versus 1.6 days), a signature of rotational braking by the disk, albeit with small numbers. With an overall median period of 1.9 days, brown dwarfs in Taurus rotate slower than their counterparts in somewhat older (3-10 Myr) star-forming regions, consistent with spin-up of the latter due to contraction and angular momentum conservation, a clear sign that disk braking overall is inefficient and/or temporary in this mass domain. We confirm the presence of a linear increase of the typical rotation period as a function of mass in the substellar regime. The rotational velocities, when calculated forward to the age of the solar system, assuming angular momentum conservation, fit the known spin-mass relation for solar system planets and extra-solar planetary-mass objects. This spin-mass trend holds over six orders of magnitude in mass, including objects from several different formation paths. Our result implies that brown dwarfs by and large retain their primordial angular momentum through the first few Myr of their evolution.
We present the analysis of high-resolution optical spectra of four transits of 55Cnc e, a low-density super-Earth that orbits a nearby Sun-like star in under 18 hr. The inferred bulk density of the ...planet implies a substantial envelope, which, according to mass-radius relationships, could be either a low-mass extended or a high-mass compact atmosphere. Our observations investigate the latter scenario, with water as the dominant species. We take advantage of the Doppler cross-correlation technique, high-spectral resolution, and the large wavelength coverage of our observations to search for the signature of thousands of optical water absorption lines. Using our observations with HDS on the Subaru telescope and ESPaDOnS on the Canada-France-Hawaii Telescope, we are able to place a 3 lower limit of 10 g mol−1 on the mean-molecular weight of 55Cnc e's water-rich (volume mixing ratio >10%), optically thin atmosphere, which corresponds to an atmospheric scale-height of ∼80 km. Our study marks the first high-spectral resolution search for water in a super-Earth atmosphere, and demonstrates that it is possible to recover known water-vapor absorption signals in a nearby super-Earth atmosphere, using high-resolution transit spectroscopy with current ground-based instruments.
Abstract
We report on Fe
i
in the dayside atmosphere of the ultra-hot-Jupiter WASP-33b, providing evidence for a thermal inversion in the presence of an atomic species. We also introduce a new way to ...constrain the planet’s brightness variation throughout its orbit, including its day–night contrast and peak phase offset, using high-resolution Doppler spectroscopy alone. We do so by analyzing high-resolution optical spectra of six arcs of the planet’s phase curve, using Echelle SpectroPolarimetric Device for the Observation of Stars (ESPaDOnS) on the Canada–France–Hawaii telescope and High Dispersion Spectrograph on the Subaru telescope. By employing a likelihood mapping technique, we explore the marginalized distributions of parameterized atmospheric models, and detect Fe
i
emission at high significance (>10.4
σ
) in our combined data sets, located at
K
p
= 222.1 ± 0.4 km s
−1
and
v
sys
= −6.5 ± 0.3 km s
−1
. Our values agree with previous reports. By accounting for WASP-33b’s brightness variation, we find evidence that its nightside flux is <10% of the dayside flux and the emission peak is shifted westward of the substellar point, assuming the spectrum is dominated by Fe
i
. Our ESPaDOnS data, which cover phases before and after the secondary eclipse more evenly, weakly constrain the phase offset to +22 ± 12 degrees. We caution that the derived volume-mixing ratio depends on our choice of temperature-pressure profile, but note it does not significantly influence our constraints on day–night contrast or phase offset. Finally, we use simulations to illustrate how observations with increased phase coverage and higher signal-to-noise ratios can improve these constraints, showcasing the expanding capabilities of high-resolution Doppler spectroscopy.
Our understanding of the brown dwarf population in star-forming regions is dependent on knowing distances and proper motions and therefore will be improved through the Gaia space mission. In this ...paper, we select new samples of very low-mass objects (VLMOs) in Upper Scorpius using UKIDSS colors and optimized proper motions calculated using Gaia DR1. The scatter in proper motions from VLMOs in Upper Scorpius is now (for the first time) dominated by the kinematic spread of the region itself, not by the positional uncertainties. With age and mass estimates updated using Gaia parallaxes for early-type stars in the same region, we determine masses for all VLMOs. Our final most complete sample includes 453 VLMOs of which ∼125 are expected to be brown dwarfs. The cleanest sample is comprised of 131 VLMOs, with ∼105 brown dwarfs. We also compile a joint sample from the literature that includes 415 VLMOs, out of which 152 are likely brown dwarfs. The disk fraction among low-mass brown dwarfs ( ) is substantially higher than in more massive objects, indicating that disks around low-mass brown dwarfs survive longer than in low-mass stars overall. The mass function for is consistent with the Kroupa Initial Mass Function. We investigate the possibility that some "proper motion outliers" have undergone a dynamical ejection early in their evolution. Our analysis shows that the color-magnitude cuts used when selecting samples introduce strong bias into the population statistics due to varying levels of contamination and completeness.
We present the results of a multiplicity survey of 212 T Tauri stars in the Chamaeleon I and Taurus-Auriga star-forming regions, based on high-resolution spectra from the Magellan Clay 6.5 m ...telescope. From these data, we achieved a typical radial velocity (RV) precision of ~80 m s super(-1) with slower rotators yielding better precision, in general. For 174 of these stars, we obtained multi-epoch data with sufficient time baselines to identify binaries based on RV variations. We identified eight close binaries and four close triples, of which three and two, respectively, are new discoveries. The spectroscopic multiplicity fractions we find for Chamaeleon I (7%) and Taurus-Auriga (6%) are similar to each other, and to the results of field star surveys in the same mass and period regime. However, unlike the results from imaging surveys, the frequency of systems with close companions in our sample is not seen to depend on primary mass. Additionally, we do not find a strong correlation between accretion and close multiplicity. This implies that close companions are not likely the main source of the accretion shut down observed in weak-lined T Tauri stars. Our results also suggest that sufficient RV precision can be achieved for at least a subset of slowly rotating young stars to search for hot Jupiter planets.
Abstract
The transmission spectrum of the ultrahot Jupiter KELT-9b (
T
eq
∼ 4000 K) exhibits absorption by several metal species. We searched for atomic and molecular lines in its emission spectrum ...by observing partial phase curves with the Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrographs (
R
∼ 80,000–95,000). We find evidence for emission by Si
i
in the atmosphere of KELT-9b for the first time. Additionally we find evidence for emission by Mg
i
and Ca
ii
, which were previously detected in transmission, and confirmed earlier detections of Fe
i
emission. Conversely, we find no evidence for dayside emission from Al
i
, Ca
i
, Cr
i
, FeH, Fe
ii
, K
i
, Li
i
, Mg
ii
, Na
i
, OH, Ti
i
, TiO, V
i
, V
ii
, VO, and Y
i
. By employing likelihood mapping, we find indications of there being little variation in emission line contrast between the day- and nightsides—suggesting that KELT-9b may harbor iron emission on its nightside. Our results demonstrate that high-resolution ground-based emission spectroscopy can provide valuable insights into exoplanet atmospheres.
Abstract
We report on a sensitive infrared search for disks around isolated young planetary-mass objects (PMOs) in the NGC 1333 cluster, by stacking 70 Spitzer/IRAC frames at 3.6 and 4.5
μ
m. Our ...coadded images go >2.3 mag deeper than single-epoch frames, and cover 50 brown dwarfs, 15 of which have M9 or later spectral types. Spectral types >M9 correspond to masses in the giant-planet domain, i.e., near or below the deuterium-burning limit of 0.015
M
⊙
. Five of the 12 PMOs show definitive evidence of excess, implying a disk fraction of 42%, albeit with a large statistical uncertainty given the small sample. Comparing with measurements for higher-mass objects, the disk fraction does not decline substantially with decreasing mass in the substellar domain, consistent with previous findings. Thus, free-floating PMOs have the potential to form their own miniature planetary systems. We note that only one of the six lowest-mass objects in NGC 1333, with spectral type L0 or later, has a confirmed disk. Reviewing the literature, we find that the lowest-mass free-floating objects with firm disk detections have masses ∼0.01
M
⊙
(or ∼10
M
Jup
). It is not clear yet whether even lower-mass objects harbor disks. If not, it may indicate that ∼10
M
Jup
is the lower-mass limit for objects that form like stars. Our disk-detection experiment on deep Spitzer images paves the way for studies with JWST at longer wavelengths and higher sensitivity, which will further explore disk prevalence and formation of free-floating PMOs.
The nearby super-Earth 55 Cnc e orbits a bright (V = 5.95 mag) star with a period of ∼18 hr and a mass of ∼8M⊕. Its atmosphere may be water-rich and have a large-scale height; though, attempts to ...characterize it have yielded ambiguous results. Here we present a sensitive search for water and TiO in its atmosphere at high spectral resolution using the Gemini North telescope and the GRACES spectrograph. We combine observations with previous observations from Subaru and CFHT, improving the constraints on the presence of water vapor. We adopt parametric models with an updated planet radius based on recent measurements, and use a cross-correlation technique to maximize sensitivity. Our results are consistent with atmospheres that are cloudy or contain minimal amounts of water and TiO. Using these parametric models, we rule out a water-rich atmosphere (VMR 0.1%) with a mean molecular weight of 15 g mol−1 at a 3 confidence level, improving on the previous limit by a significant margin. For TiO, we rule out a mean molecular weight of 5 g mol−1 with a 3 confidence level for a VMR greater than 10−8; for a VMR of greater than 10−7, the limit rises to a mean molecular weight of 10 g mol−1. We can rule out low mean-molecular-weight chemical equilibrium models both including and excluding TiO/VO at very high confidence levels (>10 ). Overall, our results are consistent with an atmosphere with a high mean molecular weight and/or clouds, or no atmosphere.
Giant planets are usually thought to form within a few tens of AU of their host stars, and hence it came as a surprise when we found what appeared to be a planetary mass (~0.008 M ) companion around ...the 5 Myr old solar mass star 1RXS J160929.1 -- 210524 in the Upper Scorpius association. At the time, we took the object's membership in Upper Scorpius--established from near-infrared, H- and K-band spectroscopy--and its proximity (22 or 330 AU) to the primary as strong evidence for companionship, but could not verify their common proper motion. Here, we present follow-up astrometric measurements that confirm that the companion is indeed comoving with the primary star, which we interpret as evidence that it is a truly bound planetary mass companion. We also present new J-band spectroscopy and 3.0-3.8 Delta *mm photometry of the companion. Based on a comparison with model spectra, these new measurements are consistent with the previous estimate of the companion effective temperature of 1800 plus or minus 200 K. We present a new estimate of the companion mass based on evolution models and the calculated bolometric luminosity of the companion; we obtain a value of 0.008+0.003 --0.002 M , again consistent with our previous result. Finally, we present angular differential imaging observations of the system allowing us to rule out additional planets in the system more massive than 1 M Jup, 2 M Jup, and 8 M Jup at projected separations larger than 3'' (~440 AU), 07 (~100 AU), and 035 (~50 AU), respectively. This companion is the least massive known to date at such a large orbital distance; it shows that objects in the planetary mass range exist at orbital separations of several hundred AU, posing a serious challenge for current formation models.
With a dayside temperature in excess of 4500 K, comparable to a mid-K-type star, KELT-9b is the hottest planet known. Its extreme temperature makes KELT-9b a particularly interesting test bed for ...investigating the nature and diversity of gas giant planets. We observed the transit of KELT-9b at high spectral resolution (R ∼ 94,600) with the CARMENES instrument on the Calar Alto 3.5 m telescope. Using these data, we detect for the first time ionized calcium (Ca ii triplet) absorption in the atmosphere of KELT-9b; this is the second time that Ca ii has been observed in a hot Jupiter. Our observations also reveal prominent H absorption, confirming the presence of an extended hydrogen envelope around KELT-9b. We compare our detections with an atmospheric model and find that all four lines form between atmospheric temperatures of 6100 and 8000 K and that the Ca ii lines form at pressures between 50 and 100 nbar while the H line forms at a lower pressure (∼10 nbar), higher up in the atmosphere. The altitude that the core of H line forms is found to be ∼1.4 Rp, well within the planetary Roche lobe (∼1.9 Rp). Therefore, rather than probing the escaping upper atmosphere directly, the H line and the other observed Balmer and metal lines serve as atmospheric thermometers enabling us to probe the planet's temperature profile, thus the energy budget.
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