848 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
A New Pleiades Member at the Lithium Substellar Boundary
We present the discovery of an object in the Pleiades open cluster, named
Teide 2, with optical and infrared photometry which place it on the cluster
sequence slightly below the expected substellar mass limit. We have obtained
low- and high-resolution spectra that allow us to determine its spectral type
(M6), radial velocity and rotational broadening; and to detect H in
emission and Li I 670.8 nm in absorption. All the observed properties strongly
support the membership of Teide 2 into the Pleiades. This object has an
important role in defining the reappearance of lithium below the substellar
limit in the Pleiades. The age of the Pleiades very low-mass members based on
their luminosities and absence or presence of lithium is constrained to be in
the range 100--120 Myr.Comment: 17 pages, 3 figure
Rotational modulation of the linear polarimetric variability of the cool dwarf TVLM 51346546
Aims: We aimed to monitor the optical linear polarimetric signal of the
magnetized, rapidly rotating M8.5 dwarf TVLM 51346546.
Methods: - and -band linear polarimetry images were collected with the
ALFOSC instrument of the 2.56-m Nordic Optical Telescope on two consecutive
nights covering about 0.5 and 4 rotation cycles in the and filters,
respectively. We also obtained simultaneous intensity curves by means of
differential photometry. The typical precision of the data is 0.46\%
(), 0.35\% () in the linear polarization degree and 9 mmag
(), 1.6 mmag () in the differential intensity curves.
Results: Strong and variable linear polarization is detected in the and
filters, with values of maximum polarization ( = 1.300.35 \%)
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 TVLM 51346's surface synchronized with rotation. We found that
the peaks of the intensity and polarimetric curves occur with a phase
difference of 0.180.01, and that the maximum of the linear polarization
happens nearly half a period (0.590.03) after the radio pulse. We
discussed different scenarios to account for the observed properties of the
light curves.Comment: Accepted for publication in Astronomy and Astrophysic
Simultaneous optical and near-infrared linear spectropolarimetry of the earthshine
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 O and water vapor
are strong flux absorbents in the Earth atmosphere and some linear polarization
of the reflected stellar light is expected to occur at these wavelengths.
Methods: Simultaneous optical ( m) and near-infrared (
m) 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 atmosphere.
Results: We find the highest values of linear polarization () at
the bluest wavelengths, which agrees with the literature. Linear polarization
intensity steadily decreases towards red wavelengths reaching a nearly flat
value beyond 0.8 m. In the near-infrared, we measured a polarization
degree of for the continuum. We report the detection of molecular
features due to O at m and HO at 0.6530.725
m, 0.7800.825 m, 0.93 and 1.12 m in the spectropolarimetric
data; most of them show high linear polarimetry degrees above the continuum. In
particular, the broad HO 1.12 m band displays a polarimetric
intensity as high as that of the blue optical. These features may become a
powerful tool to characterize Earth-like planets in polarized light.Comment: 4 pages, 3 figures. Accepted for publication as Letter in Astronomy
and Astrophysics on 23/01/201
Characterization of the known T type dwarfs towards the Sigma Orionis cluster
(Abridged) A total of three T type candidates (SOri70, SOri73, and
SOriJ0538-0213) lying in the line of sight towards Sigma Orionis were
characterized by means of near-infrared photometric, astrometric, and
spectroscopic studies. H-band methane images were collected for all three
sources and an additional sample of 15 field T type dwarfs using LIRIS/WHT.
J-band spectra of resolution of ~500 were obtained for SOriJ0538-0213 with
ISAAC/VLT, and JH spectra of resolution of ~50 acquired with WFC3/HST were
employed for the spectroscopic classification of SOri70 and 73. Proper motions
with a typical uncertainty of +/-3 mas/yr and a time interval of ~7-9 yr were
derived. Using the LIRIS observations of the field T dwarfs, we calibrated this
imager for T spectral typing via methane photometry. The three SOri objects
were spectroscopically classified as T4.5+/-0.5 (SOri73), T5+/-0.5
(SOriJ0538-0213), and T7 (SOri70). The similarity between the
observed JH spectra and the methane colors and the data of field ultra-cool
dwarfs of related classifications suggests that SOri70, 73, and
SOriJ053804.65-021352.5 do not deviate significantly in surface gravity in
relation to the field. Additionally, the detection of KI at ~1.25 microns in
SOriJ0538-0213 points to a high-gravity atmosphere. Only the K-band reddish
nature of SOri70 may be consistent with a low gravity atmosphere. The proper
motions of SOri70 and 73 are measurable and are larger than that of the cluster
by >3.5 sigma. The proper motion of SOriJ0538-0213 is consistent with a null
displacement. These observations suggest that none of the three T dwarfs are
likely Sigma Orionis members, and that either planetary-mass objects with
masses below ~4 MJup may not exist free-floating in the cluster or they may lie
at fainter near-infrared magnitudes than those of the targets (this is H>20.6
mag), thus remaining unidentified to date.Comment: Accepted for publication in A&A (2014), corrected typo
Ultra low-mass star and substellar formation in sigma Orionis
The nearby young sigma Orionis cluster (~360 pc, ~3 Ma) is becoming one of
the most important regions for the study of ultra low-mass star formation and
its extension down to the mass regimes of the brown dwarfs and planetary-mass
objects. Here, I introduce the sigma Orionis cluster and present three studies
that the JOVIAN group is developing: a pilot programme of near-infrared
adaptive-optics imaging, intermediate-resolution optical spectroscopy of a
large sample of stars of the cluster and a study of the mass function down to
the planetary-mass domain. This paper is a summary of the content of four
posters that I presented in the Ultra low-mass star formation and evolution
Workshop, as single author or on behalf of different collaborations.Comment: 4 pages, 4 figures. Proceeding at the IAC-TNG Workshop on Ultra
low-mass star formation and evolution, 28 June - 1 July 2005, La Palma,
Canary Islands, Spain. Accepted for publication in Astron. Nach
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