55 research outputs found
Long-term K-band photometric monitoring of L dwarfs
(abridged) We perform photometric time-series analysis of a sample of ten
early to mid-L dwarfs in the field over three years of -band observations
with the OMEGA 2000 infrared camera of the 3.5m telescope on Calar Alto
Observatory between January 2010 and December 2012. We perform -band
differential photometry of our targets (with typical errors of 15-30~mmag
at the 1 level) by subtracting a reference flux from each photometric
measurement. This reference flux is computed using three nearby, probably
constant stars in the target's field-of-view. We then construct and visually
inspect the light curves to search for variability, and use four different
periodogram algorithms to look for possible periods in our photometric data.
Our targets do not display long-term variability over 1 compared to
other nearby stars of similar brightness, nor do the periodograms unveil any
possible periodicity for these objects, with two exceptions:
2MASS~J02411151-0326587 and G196-3B. In the case of 2MASS~J02411151-0326587
(L0), our data suggest a tentative period of 30721~days, at 40% confidence
level, which seems to be associated with peak-to-peak variability of
4410~mmag. This object may also display variability in timescales of
years, as suggested by the comparison of our Ks-band photometry with 2MASS. For
G196-3B (L3), we find peak-to-peak variations of 4210~mmag, with a
possible photometric period of 4427~days, at 95% confidence level. This is
roughly the double of the astrometric period reported by Zapatero Osorio
(2014). Given the significance of these results, further photometric data are
required to confirm the long-term variability.These results suggest that early-
to mid-L dwarfs are fairly stable in the -band within 90 mmag at the
3 level over months to years, which covers hundreds to tens of
thousands of rotation cycles.Comment: Accepted for publication in Astronomy & Astrophysic
Linear polarization of rapidly rotating ultracool dwarfs
Aims. We aim at studying the near infrared linear polarization signal of
rapidly rotating ultracool dwarfs with spectral types ranging from M7 through
T2 and projected rotational velocities vsini >= 30 km s^{-1}. All these dwarfs
are believed to have dusty atmospheres and oblate shapes, 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, five of which were also observed in the
Z-band using the LIRIS spectrograph 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 of >=3\sigma.\\ 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 independently of spectral type and spectroscopic rotational
velocity. However, simple statistics point at the fastest rotators (vsini >=60
km s^{-1}) having a larger fraction of positive detections and a larger
averaged linear polarization degree than the moderately rotating dwarfs
(vsini=30--60 km s^{-1}). Our data suggest little linear polarimetric
variability on short time scales (i.e., observations separated by a few ten
rotation periods), and significant variability on long time scales (i.e.,
hundred to thousand rotation cycles), supporting the presence of "long-term
weather" in ultracool dwarf atmospheres.Comment: 12 pages, 7 figures, recommended for publication in Astronomy and
Astrophysic
A low-mass triple system with a wide L/T transition brown dwarf component: NLTT 51469AB/SDSS 2131-0119
We demonstrate that the previously identified L/T transition brown dwarf SDSS J213154.43-011939.3 (SDSS 2131-0119) is a widely separated (82 ''.3, similar to 3830 au) common proper motion companion to the low-mass star NLTT 51469, which we reveal to be a close binary itself, separated by 0 ''.64 +/- 0 ''.01 (similar to 30 au). We find the proper motion of SDSS 2131-0119 of mu(alpha) cos delta = -100 +/- 20 mas yr(-1) and mu(delta) = -230 +/- 20 mas yr(-1) consistent with the proper motion of the primary provided by Gaia DR2: mu(alpha) cos delta = -95.49 +/- 0.96 mas yr(-1) and mu(delta) = -239.38 +/- 0.96 mas yr(-1). Based on optical and near-infrared spectroscopy, we classify the primary NLTT 51469A as an M3 +/- 1 dwarf, estimate photometrically the spectral type of its close companion NLTT 51469B at similar to M6, and confirm the spectral type of the brown dwarf to be L9 +/- 1. Using radial velocity, proper motion, and parallax, we derived the UVW Galactic space velocities of NLTT 51469A, showing that the system does not belong to any known young stellar moving group. The high V, W velocities, lack of a 670.8 nm Li I absorption line, and absence of H alpha emission, detected X-rays, or UV excess, indicate that the system is likely a member of the thin disc population and is older than 1 Gyr. For the parallactic distance of 46.6 +/- 1.6 pc from Gaia DR2, we determined luminosities of -1.50(-0.04)(+0.02) and -4.4 +/- 0.1 dex of the M3 and L9, respectively. Considering the spectrophotometric estimation, which yields a slightly lower distance of 34(-13)(+10) pc, the obtained luminosities are -1.78(-0.04)(+0.02) and -4.7(-0.5)(+0.3) dex. We also estimated their effective temperatures and masses, and obtained 3410(-210)(+140) K and 0.42 +/- 0.02 M-circle dot for the primary, and 1400-1650K and 0.05-0.07 M-circle dot for the wide companion. For the similar to M6 component, we estimated T-eff = 2850 +/- 200 K and m = 0.10(-0.01)(+0.06) M-circle dot.BG acknowledges support from the CONICYT through FONDECYT Postdoctoral Fellowship grant no. 3170513. This work is partly financed by the Spanish Ministry of Economy and Competitiveness through the project AYA2016-79425-C3-2-P. NL and VJSB acknowledge support from the SpanishMinistry of Economy and Competitivity through the project AYA2015-69350-C3-2-P. AP acknowledges support from the Spanish Ministry of Economy and Competitivity through the project AYA2015-69350-C3-3-P. Based on observations obtained as part of the VHS, ESO programme, 179.A-2010 (PI: McMahon). Based on observations collected at the European Organisation for Astronomical Research in the Southern hemisphere under ESO programme 092.C-0874(B). Based on observations made with the NOT, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. This paper includes data obtained using the 6.5 m Magellan Clay Telescope at Las Campanas Observatory, Chile. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium).Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research has made use of NASA's Astrophysics Data System. We have made use of the ROSAT Data Archive of the Max-Planck-Institut fur extraterrestrische Physik (MPE) at Garching, Germany. This research has made use of theWashington Double Star Catalog maintained at the U.S. Naval Observatory
New constraints on the presence of debris disks around G 196-3 B and VHS J125601.92â125723.9 b
Context. The existence of warm (protoplanetary) disks around very young isolated planetary and brown dwarf mass objects is known based on near- and mid-infrared flux excesses and millimeter observations. These disks may later evolve into debris disks or rings, although none have been observed or confirmed so far. Little is known about circum(sub)stellar and debris disks around substellar objects.
Aims. We aim to investigate the presence of debris disks around two of the closest (~20 pc), young substellar companions, namely G196-3 B and VHS J125601.92â125723.9 b (VHS J1256â1257 b), whose masses straddle the borderline between planets and brown dwarfs. Both are companions at wide orbits (â„100 au) of M-type dwarfs and their ages (50â100 Myr and 150â300 Myr, respectively) are thought to be adequate for the detection of second-generation disks.
Methods. We obtained deep images of G196-3 B and VHS J1256â1257 b with the NOrthern Extended Millimeter Array (NOEMA) at 1.3 mm. These data were combined with recently published Atacama Large Millimeter Array (ALMA) and Very Large Array (VLA) data of VHS J1256â1257 b at 0.87 mm and 0.9 cm, respectively.
Results. Neither G196-3 B nor VHS J1256â1257 b were detected in the NOEMA, ALMA, and VLA data. At 1.3 mm, we imposed flux upper limits of 0.108 mJy (G196-3 B) and 0.153 mJy (VHS J1256â1257 b) with a 3-Ï confidence. Using the flux upper limits at the millimeter and radio wavelength regimes, we derived maximum values of 1.38Ă10â2 MEarth and 5.46 Ă 10â3 MEarth for the mass of any cold dust that might be surrounding G196-3 B and VHS J1256â1257 b, respectively.
Conclusions. We put our results in the context of other deep millimeter observations of free-floating and companion objects with substellar masses smaller than 20 MJup and ages between approximately one and a few hundred million years. Only two very young (2â5.4 Myr) objects are detected out of a few tens of them. This implies that the disks around these very low-mass objects must have small masses, and possibly reduced sizes, in agreement with findings by other groups. If debris disks around substellar objects scale down (in mass and size) in a similar manner as protoplanetary disks do, millimeter observations of moderately young brown dwarfs and planets must be at least two orders of magnitude deeper to be able to detect and characterize their surrounding debris disks
The Monitor project: JW 380 - a 0.26-, 0.15-Mâ, pre-main-sequence eclipsing binary in the Orion nebula cluster
We report the discovery of a low-mass (0.26 ± 0.02, 0.15 ± 0.01 Mâ) pre-main-sequence (PMS) eclipsing binary (EB) with a 5.3 d orbital period. JW 380 was detected as part of a high-cadence time-resolved photometric survey (the Monitor project) using the 2.5-m Isaac Newton Telescope and Wide Field Camera for a survey of a single field in the Orion nebula cluster (ONC) region in V and i bands. The star is assigned a 99 per cent membership probability from proper motion measurements, and radial velocity observations indicate a systemic velocity within 1Ï of that of the ONC. Modelling of the combined light and radial velocity curves of the system gave stellar radii of for the primary and the secondary, with a significant third light contribution which is also visible as a third peak in the cross-correlation functions used to derive radial velocities. The masses and radii appear to be consistent with stellar models for 2-3 Myr age from several authors, within the present observational errors. These observations probe an important region of mass-radius parameter space, where there are currently only a handful of known PMS EB systems with precise measurements available in the literatur
IAA : InformaciĂłn y actualidad astronĂłmica (31)
Sumario : RelĂĄmpagos en las alturas.--
El misterio de Di Herculis.--
Jets en galaxias activas.--
HISTORIAS DE ASTRONOMĂA. Los All-Star de la fĂsica.--
DECONSTRUCCIĂN Y otros ENSAYOS. CĂłmo âencenderâ un cuĂĄsar .--
EL âMOBY DICKâ DE... MarĂa Rosa Zapatero Osorio (CAB, CSIC-INTA).--
ACTUALIDAD.--
ENTRE BASTIDORES.--
CIENCIA: PILARES E INCERTIDUMBRES :
El Sistema Solar: Âżconocemos de verdad nuestro vecindario?.--
ACTIVIDADES IAA, AGENDA Y RECOMENDADOS.N
Characterization of the K2-38 planetary system: Unraveling one of the densest planets known to date
.-- Toledo-PadrĂłn, B. et al.Context. An accurate characterization of the known exoplanet population is key to understanding the origin and evolution of planetary systems. Determining true planetary masses through the radial velocity (RV) method is expected to experience a great improvement thanks to the availability of ultra-stable echelle spectrographs. Aims. We took advantage of the extreme precision of the new-generation echelle spectrograph ESPRESSO to characterize the transiting planetary system orbiting the G2V star K2-38 located at 194 pc from the Sun with V 11.4. This system is particularly interesting because it could contain the densest planet detected to date. Methods. We carried out a photometric analysis of the available K2 photometric light curve of this star to measure the radius of its two known planets, K2-38b and K2-38c, with Pb = 4.01593 ± 0.00050 d and Pc = 10.56103 ± 0.00090 d, respectively. Using 43 ESPRESSO high-precision RV measurements taken over the course of 8 months along with the 14 previously published HIRES RV measurements, we modeled the orbits of the two planets through a Markov chain Monte Carlo analysis, significantly improving their mass measurements. Results. Using ESPRESSO spectra, we derived the stellar parameters, Teff = 5731 ± 66, log g = 4.38 ± 0.11 dex, and [Fe/H] = 0.26 ± 0.05 dex, and thus the mass and radius of K2-38, Ma = 1.03-0.02+0.04 MaS and Ra = 1.06-0.06+0.09 RaS. We determine new values for the planetary properties of both planets. We characterize K2-38b as a super-Earth with RP = 1.54 ± 0.14 RaS and Mp = 7.3-1.0+1.1 MaS, and K2-38c as a sub-Neptune with RP = 2.29 ± 0.26 RaS and Mp = 8.3-1.3+1.3 MaS. Combining the radius and mass measurements, we derived a mean density of Ïp = 11.0-2.8+4.1 g cm-3 for K2-38b and Ïp = 3.8-1.1+1.8 g cm-3 for K2-38c, confirming K2-38b as one of the densest planets known to date. Conclusions. The best description for the composition of K2-38b comes from an iron-rich Mercury-like model, while K2-38c is better described by a rocky-model with H2 envelope. The maximum collision stripping boundary shows how giant impacts could be the cause for the high density of K2-38b. The irradiation received by each planet places them on opposite sides of the radius valley. We find evidence of a long-period signal in the RV time-series whose origin could be linked to a 0.25-3 MJ planet or stellar activity.With funding from the Spanish government through the "MarĂa de Maeztu Unit of Excellence" accreditation (MDM-2017-0737
TOI-1201 b: A mini-Neptune transiting a bright and moderately young M dwarf
Kossakowski, D., et al.We present the discovery of a transiting mini-Neptune around TOI-1201, a relatively bright and moderately young early M dwarf (J â 9.5 mag, ~600-800 Myr) in an equal-mass ~8 arcsecond-wide binary system, using data from the Transiting Exoplanet Survey Satellite, along with follow-up transit observations. With an orbital period of 2.49 d, TOI-1201 b is a warm mini-Neptune with a radius of Rb = 2.415 ± 0.090 Râ. This signal is also present in the precise radial velocity measurements from CARMENES, confirming the existence of the planet and providing a planetary mass of Mb = 6.28 ± 0.88 Mâ and, thus, an estimated bulk density of 2.45-0.42+0.48 g cm-3. The spectroscopic observations additionally show evidence of a signal with a period of 19 d and a long periodic variation of undetermined origin. In combination with ground-based photometric monitoring from WASP-South and ASAS-SN, we attribute the 19 d signal to the stellar rotation period (Prot = 19-23 d), although we cannot rule out that the variation seen in photometry belongs to the visually close binary companion. We calculate precise stellar parameters for both TOI-1201 and its companion. The transiting planet is anexcellent target for atmosphere characterization (the transmission spectroscopy metric is 97-16+21) with the upcoming James Webb Space Telescope. It is also feasible to measure its spin-orbit alignment via the Rossiter-McLaughlin effect using current state-of-the-art spectrographs with submeter per second radial velocity precision.Part of this work was supported by the German Deutsche Forschungsgemeinschaft (DFG) project number Ts 17/2â1. CARMENES is an instrument at the Centro AstronĂłmico Hispano-AlemĂĄn (CAHA) at Calar Alto (AlmerĂa, Spain), operated jointly by the Junta de AndalucĂa and the Instituto de AstrofĂsica de AndalucĂa (CSIC). CARMENES was funded by the Max-Planck-Gesellschaft (MPG), the Consejo Superior de Investigaciones CientĂficas (CSIC), the Ministerio de EconomĂa y Competitividad (MINECO) and the European Regional Development Fund (ERDF) through projects FICTS-2011-02, ICTS-2017-07-CAHA-4, and CAHA16-CE-3978, and the members of the CARMENES Consortium (Max-Planck-Institut fĂŒr Astronomie, Instituto de AstrofĂsica de AndalucĂa, Landessternwarte Königstuhl, Institut de CiĂšncies de lâEspai, Institut fĂŒr Astrophysik Göttingen, Universidad Complutense de Madrid, ThĂŒringer Landessternwarte Tautenburg,Instituto de AstrofĂsica de Canarias, Hamburger Sternwarte, Centro de AstrobiologĂa and Centro AstronĂłmico Hispano-AlemĂĄn), with additional contributions by the MINECO, the Deutsche Forschungsgemeinschaft through the Major Research Instrumentation Programme and Research Unit FOR2544 âBlue Planets around Red Starsâ, the Klaus Tschira Stiftung, the states of Baden-WĂŒrttemberg and Niedersachsen, and by the Junta de AndalucĂa. This work was based on data from the CARMENES data archive at CAB (CSIC-INTA). We acknowledgefinancial support from the Agencia Estatal de InvestigaciĂłn of the Ministerio de Ciencia, InnovaciĂłn y Universidades and the ERDF through projects PID2019-109522GB-C5[1:4]/AEI/10.13039/501100011033 and the Centre of Excellence âSevero Ochoaâ and âMarĂa de Maeztuâ awards to the Instituto de AstrofĂsica de Canarias (SEV-2015-0548), Instituto de AstrofĂsica de AndalucĂa (SEV-2017-0709), and Centro de AstrobiologĂa (MDM-2017-0737), the European Research Council under the Horizon 2020 Framework Program (ERC Advanced Grant Origins 83 24 28), the Generalitat de Catalunya/CERCA programme, the DFG priority program SPP 1992 âExploring the Diversity of Extrasolar Planets (JE 701/5-1)â, the European Research Council under the Horizon 2020 Framework Program via ERC Advanced Grant Origins 832428 and under Marie SkĆodowska-Curie grant 895525
TOI-1801 b: A temperate mini-Neptune around a young M0.5 dwarf
MallorquĂn, M., et al.We report the discovery, mass, and radius determination of TOI-1801 b, a temperate mini-Neptune around a young M dwarf. TOI-1801 b was observed in TESS sectors 22 and 49, and the alert that this was a TESS planet candidate with a period of 21.3 days went out in April 2020. However, ground-based follow-up observations, including seeing-limited photometry in and outside transit together with precise radial velocity (RV) measurements with CARMENES and HIRES revealed that the true period of the planet is 10.6 days. These observations also allowed us to retrieve a mass of 5.74 ± 1.46 Mâ, which together with a radius of 2.08 ± 0.12 Râ, means that TOI-1801 b is most probably composed of water and rock, with an upper limit of 2% by mass of H2 in its atmosphere. The stellar rotation period of 16 days is readily detectable in our RV time series and in the ground-based photometry. We derived a likely age of 600â800 Myr for the parent star TOI-1801, which means that TOI-1801 b is the least massive young mini-Neptune with precise mass and radius determinations. Our results suggest that if TOI-1801 b had a larger atmosphere in the past, it must have been removed by some evolutionary mechanism on timescales shorter than 1 Gyr.This work is partly financed by the Spanish Ministry of Economics and Competitiveness through projects PGC2018-098153-B-C31, PID2019-109522GB-C5[1:4]. E. G. acknowledges the generous support from the Deutsche Forschungsgemeinschaft (DFG) of the grant HA3279/14-1. P.D. acknowledges support from a 51 Pegasi b Postdoctoral Fellowship from the Heising-Simons Foundation. D.H. acknowledges support from the Alfred P. Sloan Foundation, the National Aeronautics and Space Administration (80NSSC21K0652) and the Australian Research Council (FT200100871). This work is partly supported by JSPS KAKENHI Grant Numbers JP18H05439 and JST CREST Grant Number JPMJCR176.Peer reviewe
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