Abstract
We aim to study the optical and near-infrared linear polarimetric properties of a sample of young M7–L7 dwarfs (≈ 1–500 Myr) with spectroscopic signatures of low- and intermediate-gravity ...atmospheres. We collected optical (RIZ) and near-infrared (YJHK
s) linear polarimetry images on various time-scales from ∼0.2 h to months. Linear polarization degrees in the interval 0–1.5 per cent (I and J bands) were measured with accuracies ranging from ±0.1 to ±0.9 per cent depending on the observing filter and the target brightness. We found that the young field dwarfs in our sample show similar polarimetric degrees at both I and J bands, and that there is no obvious trend with the spectral type. The two Taurus sources in our sample show intense levels of J-band linear polarization probably due to surrounding discs. By compiling data from the literature for high-gravity M7–L7 dwarfs with likely ages ≥500 Myr, we did not observe any apparent difference in the linear polarimetry intensity between the young and old samples that could be ascribed to differing atmospheric gravities. Polarimetric variability with peak to peak amplitudes up to 1.5 per cent is detected on scales of about a rotation in two out of four targets that were monitored over several hours. Long-term polarimetric variability is also detected in nearly all dwarfs of the sample with data spanning months to years.
Aims. We aim to extend our current observational understanding of the integrated planet Earth spectropolarimetry from the optical to the near-infrared wavelengths. Major biomarkers like O2 and water ...vapor are strong flux absorbents in the Earth’s atmosphere, and some linear polarization of the reflected stellar light is expected to occur at these wavelengths. Methods. Simultaneous optical (0.4−0.9 μm) and near-infrared (0.9−2.3 μm) linear spectropolarimetric data of the earthshine were acquired by observing the nightside of the waxing Moon. The data have sufficient spectral resolution (2.51 nm in the optical, and 1.83 and 2.91 nm in the near-infrared) to resolve major molecular species present in the Earth’s atmosphere. Results. We find the highest values of linear polarization (≥10%) at the bluest wavelengths, which agrees with other studies. Linear polarization intensity steadily decreases toward red wavelengths reaching a nearly flat value beyond ~0.8 μm. In the near-infrared, we measured a polarization degree of ~4.5 % for the continuum. We report the detection of molecular features due to O2 at 0.760,1.25 μm, and H2O at 0.653–0.725 μm, 0.780–0.825 μm, 0.93, and 1.12 μm in the spectropolarimetric data, and most of them show high linear polarimetry degrees above the continuum. In particular, the broad H2O 1.12 μm band displays a polarimetric intensity as high as that of the blue optical. These features may become a powerful tool for characterizing Earth-like planets in polarized light.
Aims. We aim to determine the trigonometric parallaxes and proper motions of a sample of ten field L0–L5 dwarfs with spectroscopic evidence for low-gravity atmospheres. The ten sources were located ...in color-absolute magnitude diagrams and in the Hertzsprung-Russell (HR) diagram for age and mass derivations and were compared with field and star cluster dwarfs of related spectral classification and with state-of-the-art solar-metallicity evolutionary models. Methods. We obtained J and Ks imaging data using 2–4 m class telescopes with a typical cadence of one image per month between 2010 January and 2012 December, in which the data cover a time baseline of nearly three years. We also obtained low resolution optical spectra (R ~ 300, 500–1100 nm) using the 10 m Gran Telescopio de Canarias to assess the presence of lithium absorption in four targets and confirm their young age. The derived parallaxes and proper motions were combined with data from the literature to determine Teff, luminosity, and space velocities. All this information along with the lithium observations was used to assess the ages and masses of the sample. The astrometric curves were also examined for periodic perturbations indicative of unseen companions. Results. Trigonometric parallaxes and proper motions were derived to typical accuracies of a milliarcsecond (mas) and ±10 mas yr-1, respectively. All ten L dwarfs have large motions (μ ≥ 70 mas yr-1) and are located at distances between 9 and 47 pc. They lie above and on the sequence of field dwarfs in the diagrams of absolute J and Ks magnitude versus spectral type and luminosity versus effective temperature, which implies ages similar to or smaller than those typical of the field. In the HR diagram, 2MASS J00332386−1521309 (L4), 2MASS J00452143+1634446 (L2), 2MASS J03552337+1133437 (L5), 2MASS J05012406−0010452 (L4), G 196–3B (L3), 2MASS J17260007+1538190 (L3), and 2MASS J22081363+2921215 (L3) occupy locations that are compatible with the most likely ages in the interval ≈10–500 Myr if they are single objects. All of these dwarfs (except for 2MASS J00332386−1521309) show strong lithium absorption at 670.8 nm, thus confirming the young ages and masses ranging from ≈11 through ≈45 MJup for this subsample. The detection of atomic lithium in the atmosphere of 2MASS J00452143+1634446 (L2) is reported for the first time. The lack of lithium in 2MASS J00332386−1521309 (L4) is not compatible with its position in the HR diagram, suggesting a spectral type earlier than L4. The remaining three dwarfs, 2MASS J02411151−0326587 (L0), 2MASS J10224821+5825453 (L1), and 2MASS J15525906+2948485 (L0) have locations in the HR diagram indicative of older ages and higher masses consistent with the observed lithium depletion previously published. The dynamical studies based on space velocities derived from our parallaxes and proper motions fully support the aforementioned results for 2MASS J00452143+1634446, 2MASS J03552337+1133437, G 196–3B, 2MASS J10224821+5825453, and 2MASS J15525906+2948485. We did not find evidence for the presence of astrometric companions with minimum detectable masses that are typically ≥25 MJup and face-on, circular orbits with periods between 60–90 d and 3 yr around eight targets. Conclusions. The astrometric and spectroscopic data indicate that about 60–70% of the field L-type dwarfs in our sample with evidence for low-gravity atmospheres are indeed young-to-intermediate-age brown dwarfs of the solar neighborhood with expected ages and masses in the intervals ≈10–500 Myr and ≈11–45 MJup. The peaked-shape of the H-band spectra of L dwarfs, a signpost of youth, appears to be present up to ages of 120–500 Myr and intermediate-to-high gravities.
Aims. We aim to monitor the optical linear polarimetric signal of the magnetized, rapidly rotating M8.5 dwarf TVLM 513−46546. Methods. R- and I-band linear polarimetry images were collected with the ...Andalucía Faint Object Spectrograph and Camera (ALFOSC) instrument of the 2.56-m Nordic Optical Telescope (NOT) on two consecutive nights, covering about 0.5 and four rotation cycles in the R and I filters, respectively. We also obtained simultaneous intensity curves by means of differential photometry. The typical precision of the data is ±0.46% (R), ±0.35% (I) in the linear polarization degree and ±9 mmag (R), ±1.6 mmag (I) in the differential intensity curves. Results. Strong and variable linear polarization is detected in the R and I filters, with values of maximum polarization (p∗ = 1.30 ± 0.35 %), that are similar for both bands. The intensity and the polarimetric curves present a sinusoid-like pattern with a periodicity of ~1.98 h, which we ascribe to structures in the surface of TVLM 513−46546 synchronized with its rotation. We found that the peaks of intensity and polarimetric curves occur with a phase difference of 0.18 ± 0.01 and that the maximum of the linear polarization occurs nearly half a period (0.59 ± 0.03) after the radio pulse. We discuss different scenarios to account for the observed properties of the light curves.
The Earth's albedo is a fundamental climate parameter for understanding the radiation budget of the atmosphere. It has been traditionally measured not only from space platforms but also from the ...ground for 16 years from Big Bear Solar Observatory by observing the Moon. The photometric ratio of the dark (earthshine) to the bright (moonshine) sides of the Moon is used to determine nightly anomalies in the terrestrial albedo, with the aim of quantifying sustained monthly, annual, and/or decadal changes. We find two modest decadal scale cycles in the albedo, but with no significant net change over the 16 years of accumulated data. Within the evolution of the two cycles, we find periods of sustained annual increases, followed by comparable sustained decreases in albedo. The evolution of the earthshine albedo is in remarkable agreement with that from the Clouds and the Earth's Radiant Energy System instruments, although each method measures different slices of the Earth's Bond albedo.
Key Points
We presente a new 16 year long global albedo record (a fundamental climate parameter) taken using the earthshine methodolgy
The Earth's reflectance presents decadal variability, but overall no long‐term trend is identified
The new data seem to agree well with the only other available albedo data set, the one from CERES instrumentation
We report on the near-infrared (JHK-bands) low-resolution spectroscopy and red optical (Z-band) photometry of seven proper-motion, very low-mass substellar member candidates of the Pleiades cluster ...with magnitudes in the interval J = 17.5−20.8 and K = 16.1−18.5 mag. Spectra were acquired for six objects with the LIRIS and NIRSPEC instruments mounted on the 4.2-m William Herschel and the 10-m Keck II telescopes, respectively. Z-band images of two of the faintest candidates were collected with the ACAM instrument on the WHT. The new data confirm the low temperatures of all seven Pleiades proper motion candidates. From the imaging observations, we find extremely red Z − J and Z − K colors that suggest that the faintest target, Calar Pleiades 25, has a Galactic rather than extragalactic nature. We tentatively classify the spectroscopic targets from early-L to ~T0 and suggest that the L/T transition, which accounts for the onset of methane absorption at 2.1 μm, may take place at J ≈ 20.3 and K ≈ 17.8 mag in the Pleiades (absolute values of MJ ≈ 14.7 and MK ≈ 12.2 mag). We find evidence of likely low-gravity atmospheres based on the presence of triangular-shape H-band fluxes and the high flux ratio K/H (compatible with red H − K colors) of Calar Pleiades 20, 21, and 22, which is a feature also seen in field low-gravity dwarfs. Weak K i absorption lines at around 1.25 μm are probably seen in two targets. These observations add support to the cluster membership of all seven objects in the Pleiades. The trend delineated by the spectroscopic sequence of Pleiades late-M and L dwarfs resembles that of the field. With masses estimated at 0.012−0.015 M⊙ (solar metallicity and 120 Myr), Calar Pleiades 20 (L6±1), 21 (L7±1), and 22 (L/T) may become the coolest and least massive Pleiades members that are corroborated with photometry, astrometry, and spectroscopy. Calar Pleiades 25 (<0.012 M⊙) is a firm free-floating planetary-mass candidate in the Pleiades.
Aims. We aim to study the near-infrared linear polarization signal of rapidly rotating ultracool dwarfs with spectral types ranging from M7 through T2 and projected rotational velocities of v sin ...i ≳ 30 km s-1. These dwarfs are believed to have dusty atmospheres and oblate shapes, which is an appropriate scenario to produce measurable linear polarization of the continuum light. Methods. Linear polarimetric images were collected in the J-band for a sample of 18 fast-rotating ultracool dwarfs, of which five were also observed in the Z-band using the Long-slit Intermediate Resolution Infrared Spectrograph (LIRIS) on the Cassegrain focus of the 4.2-m William Herschel Telescope. The measured median uncertainty in the linear polarization degree is ±0.13% for our sample, which allowed us to detect polarization signatures above ~0.39% with a confidence interval of ≥3σ. Results. About 40 ± 15% of the sample is linearly polarized in the Z- and J-bands. All positive detections have linear polarization degrees ranging from 0.4% to 0.8% in both filters independent of spectral type and spectroscopic rotational velocity. However, simple statistics point at the fastest rotators (v sin i ≳ 60 km s-1) having a larger fraction of positive detections and a larger averaged linear polarization degree than the moderately rotating dwarfs (v sin i = 30–60 km s-1). Our data suggest little linear polarimetric variability on short timescales (i.e., observations separated by a few ten rotation periods), and significant variability on long timescales (i.e., hundred to thousand rotation cycles), supporting the presence of long-term weather in ultracool dwarf atmospheres.
ABSTRACT We present the discovery of a transiting exoplanet candidate in the K2 Field-1 with an orbital period of 9.1457 hr: K2-22b. The highly variable transit depths, ranging from ∼0% to 1.3%, are ...suggestive of a planet that is disintegrating via the emission of dusty effluents. We characterize the host star as an M-dwarf with Teff 3800 K. We have obtained ground-based transit measurements with several 1-m class telescopes and with the GTC. These observations (1) improve the transit ephemeris; (2) confirm the variable nature of the transit depths; (3) indicate variations in the transit shapes; and (4) demonstrate clearly that at least on one occasion the transit depths were significantly wavelength dependent. The latter three effects tend to indicate extinction of starlight by dust rather than by any combination of solid bodies. The K2 observations yield a folded light curve with lower time resolution but with substantially better statistical precision compared with the ground-based observations. We detect a significant "bump" just after the transit egress, and a less significant bump just prior to transit ingress. We interpret these bumps in the context of a planet that is not only likely streaming a dust tail behind it, but also has a more prominent leading dust trail that precedes it. This effect is modeled in terms of dust grains that can escape to beyond the planet's Hill sphere and effectively undergo "Roche lobe overflow," even though the planet's surface is likely underfilling its Roche lobe by a factor of 2.
Aims. With available Virtual Observatory tools, we looked for new M dwarfs in the solar neighbourhood and M giants with high tangential velocities. Methods. From an all-sky cross-match between the ...optical Tycho-2 and the near-infrared 2MASS catalogues, we selected objects with proper motions μ > 50 mas yr-1 and very red VT − Ks colours. For the most interesting targets, we collected multi-wavelength photometry, constructed spectral energy distributions, estimated effective temperatures and surface gravities from fits to atmospheric models, performed time-series analysis of ASAS V-band light curves, and assigned spectral types from low-resolution spectroscopy obtained with CAFOS at the 2.2 m Calar Alto telescope. Results. We got a sample of 59 bright red high proper-motion objects, including fifty red giants, four red dwarfs, and five objects reported in this work for the first time. The five new stars have magnitudes VT ≈ 10.8–11.3 mag, reduced proper motions midway between known dwarfs and giants, near-infrared colours typical of giants, and effective temperatures Teff ≈ 2900–3400 K. From our time-series analysis, we discovered a long secondary period in Ruber 4 and an extremely long primary period in Ruber 6. With the CAFOS spectra, we confirmed the red giant nature of Ruber 7 and 8, the last of which seems to be one of the brightest metal-poor M giants ever identified.
We report the discovery and characterization of the transiting extrasolar planet TOI-1710 b. It was first identified as a promising candidate by the Transiting Exoplanet Survey Satellite. Its ...planetary nature was then established with SOPHIE and HARPS-N spectroscopic observations via the radial-velocity method. The stellar parameters for the host star are derived from the spectra and a joint Markov chain Monte-Carlo adjustment of the spectral energy distribution and evolutionary tracks of TOI-1710. A joint MCMC analysis of the TESS light curve and the radial-velocity evolution allows us to determine the planetary system properties. From our analysis, TOI-1710 b is found to be a massive warm super-Neptune (
M
p
= 28.3 ± 4.7
M
⊕
and
R
p
= 5.34 ± 0.11
R
⊕
) orbiting a G5V dwarf star (
T
eff
= 5665 ± 55 K) on a nearly circular 24.3-day orbit (
e
= 0.16 ± 0.08). The orbital period of this planet is close to the estimated rotation period of its host star
P
rot
= 22.5 ± 2.0 days and it has a low Keplerian semi-amplitude
K
= 6.4 ± 1.0 m s
−1
; we thus performed additional analyses to show the robustness of the retrieved planetary parameters. With a low bulk density of 1.03 ± 0.23 g cm
−3
and orbiting a bright host star (
J
= 8.3,
V
= 9.6), TOI-1710 b is one of the best targets in this mass-radius range (near the Neptunian desert) for atmospheric characterization via transmission spectroscopy, a key measurement in constraining planet formation and evolutionary models of sub-Jovian planets.
PDF
