140 research outputs found
High-Resolution Spectroscopy during Eclipse of the Young Substellar Eclipsing Binary 2MASS 0535-0546. II. Secondary Spectrum: No Evidence that Spots Cause the Temperature Reversal
We present high-resolution optical spectra of the young brown-dwarf eclipsing
binary 2M0535-05, obtained during eclipse of the higher-mass (primary) brown
dwarf. Combined with our previous spectrum of the primary alone (Paper I), the
new observations yield the spectrum of the secondary alone. We investigate,
through a differential analysis of the two binary components, whether cool
surface spots are responsible for suppressing the temperature of the primary.
In Paper I, we found a significant discrepancy between the empirical surface
gravity of the primary and that inferred via fine analysis of its spectrum.
Here we find precisely the same discrepancy in surface gravity, both
qualitatively and quantitatively. While this may again be ascribed to either
cool spots or model opacity errors, it implies that cool spots cannot be
responsible for preferentially lowering the temperature of the primary: if they
were, spot effects on the primary spectrum should be preferentially larger, and
they are not. The Teff we infer for the primary and secondary, from the
TiO-epsilon bands alone, show the same reversal, in the same ratio, as is
empirically observed, bolstering the validity of our analysis. In turn, this
implies that if suppression of convection by magnetic fields on the primary is
the fundamental cause of the Teff reversal, then it cannot be a local
suppression yielding spots mainly on the primary (though both components may be
equally spotted), but a global suppression in the interior of the primary. We
briefly discuss current theories of how this might work.Comment: Final ApJ version. Small textual change in summary at the end (Sec
6.2), to include work published after submission of this paper; no changes in
our results or conclusion
Automated code for the selection of targets to be observed with the SAINT-EX telescope
In this contribution, we present the main characteristics and describe the functioning of the code developed in python language to automatically build the list of objects that are nightly observed in queue mode with the 1-m SAINT-EX telescope.Fil: Petrucci, Romina Paola. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Departamento de Astrofísica Estelar; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gómez Maqueo Chew, Yilen. Instituto de Astronomia; México. Universidad Nacional Autónoma de México; Méxic
Automated code for the selection of targets to be observed with the SAINT-EX telescope
In this contribution, we present the main characteristics and describe the functioning of the code developed in python language to automatically build the list of objects that are nightly observed in queue mode with the 1-m SAINT-EX telescope.Fil: Petrucci, Romina Paola. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Departamento de Astrofísica Estelar; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gómez Maqueo Chew, Yilen. Instituto de Astronomia; México. Universidad Nacional Autónoma de México; Méxic
A Strict Test of Stellar Evolution Models: The Absolute Dimensions of Massive Benchmark Eclipsing Binary V578 Mon
We determine the absolute dimensions of the eclipsing binary V578 Mon, a
detached system of two early B-type stars (B0V + B1V, P2.40848 d) in the
star-forming region NGC 2244 of the Rosette Nebula. From the light curve
analysis of 40 yr of photometry and the analysis of HERMES spectra, we find
radii of Rsun and Rsun, and temperatures of ~K and K respectively. We find that our
disentangled component spectra for V578 Mon agree well previous spectral
disentangling from the literature. We also reconfirm the previous spectroscopic
orbit of V578 Mon finding that masses of Msun and Msun are fully compatible with the new analysis. We compare the absolute
dimensions to the rotating models of the Geneva and Utrecht groups and the
models of Granada group. We find all three sets of models marginally reproduce
the absolute dimensions of both stars with a common age within uncertainty for
gravity-effective temperature isochrones. However - there are some apparent age
discrepancies for the corresponding mass-radius isochrones. Models with larger
convective overshoot worked best. Combined with our previously
determined apsidal motion of deg cycle,
we compute the internal structure constants (tidal Love number) for the
newtonian and general relativistic contribution to the apsidal motion,
and respectively. We find
the relativistic contribution to the apsidal motion of be small . We find
that the prediction of of the Granada
models fully agrees with our observed .Comment: accepted for publication in AJ 05/02/201
On the Abundance of Circumbinary Planets
We present here the first observationally based determination of the rate of
occurrence of circumbinary planets. This is derived from the publicly available
Kepler data, using an automated search algorithm and debiasing process to
produce occurrence rates implied by the seven systems already known. These
rates depend critically on the planetary inclination distribution: if
circumbinary planets are preferentially coplanar with their host binaries, as
has been suggested, then the rate of occurrence of planets with
orbiting with \ d is \% (95\% confidence limits),
higher than but consistent with single star rates. If on the other hand the
underlying planetary inclination distribution is isotropic, then this
occurrence rate rises dramatically, to give a lower limit of 47\%. This implies
that formation and subsequent dynamical evolution in circumbinary disks must
either lead to largely coplanar planets, or proceed with significantly greater
ease than in circumstellar disks. As a result of this investigation we also
show that giant planets () are significantly less common in
circumbinary orbits than their smaller siblings, and confirm that the proposed
shortfall of circumbinary planets orbiting the shorter period binaries in the
Kepler sample is a real effect.Comment: Accepted for publication in MNRAS (1st August 2014). 12 pages. Update
to match final version, including clarifications and new figures. Results are
unchange
Exploring the photometric variability of ultra-cool dwarfs with TESS
We present a photometric characterization of 208 ultra-cool dwarfs (UCDs)
with spectral types between M4 and L4, from 20-second and 2-minute cadence TESS
light curves. We determine rotation periods for 87 objects (42 percent) and
identify 778 flare events in 103 UCDs (49.5 percent). For 777 flaring events
(corresponding to 102 objects), we derive bolometric energies between 2.1e30
and 1.1e34 erg , with 56 superflare events. No transiting planets or eclipsing
binaries were identified. We find that the fraction of UCDs with rotation and
flaring activity is, at least, 20 percent higher in M4-M6 spectral types than
in later UCDs (M7-L4). For spectral types between M4 and L0, we measure the
slope of the flare bolometric energy-duration correlation to be gamma = 0.497
+/- 0.058, which agrees with that found in previous studies for solar-type and
M dwarfs. Moreover, we determine the slope of the flare frequency distribution
to be alpha = -1.75 +/- 0.04 for M4-M5 dwarfs, alpha = -1.69 +/- 0.04 and alpha
= -1.72 +/- 0.1 for M6-M7 and M8-L0 dwarfs, respectively, which are consistent
with previous works that exclusively analysed UCDs. These results support the
idea that independently of the physical mechanisms that produce magnetic
activity, the characteristics of the rotational modulation and flares are
similar for both fully-convective UCDs and partially-convective solar-type and
early-M stars. Based on the measured UCD flare distributions, we find that UV
radiation emitted from flares does not have the potential to start prebiotic
chemistry.Comment: Accepted for publication in MNRAS, 16 pages, 12 figure
Apsidal Motion of the Massive, Benchmark Eclipsing Binary V578 Mon
V578 Mon is a system of two early B-type stars in the Rosette Nebula
star-forming region (NGC 2244), and is one of only nine eclipsing binaries with
component masses greater than 10 M\odot whose physical parameters have been
determined with an accuracy of better than 3%. It is therefore a benchmark
system for evolutionary and stellar structure models of newly formed massive
stars. Combining our multi-band light curves spanning 40 yr with previous light
curve data from the literature, we fit a model light curve that for the first
time includes the effects of apsidal motion of the system. We measure an
apsidal period of 33.48+0.10-0.06 yr. As a consequence of incorporating the
apsidal motion into the modeling of the system's orbital parameters, we
determine an updated eccentricity of e = 0.07755+0.00022-0.00027, which differs
significantly from the value previously reported in the literature. Evidently,
the inclusion of apsidal motion in the light curve modeling significantly
affects the eccentricity determination. Incorporating these key parameters into
a comprehensive model of the system's physical parameters-including internal
structure constraints- will bring V578 Mon to the next level of benchmark
precision and utility.Comment: 17 pages, 7 figures, to appear in the Astronomical Journa
Luminosity Discrepancy in the Equal-Mass, Pre--Main Sequence Eclipsing Binary Par 1802: Non-Coevality or Tidal Heating?
Parenago 1802, a member of the ~1 Myr Orion Nebula Cluster, is a
double-lined, detached eclipsing binary in a 4.674 d orbit, with equal-mass
components (M_2/M_1 = 0.985 \pm 0.029). Here we present extensive VIcJHKs light
curves spanning ~15 yr, as well as a Keck/HIRES optical spectrum. The light
curves evince a third light source that is variable with a period of 0.73 d,
and is also manifested in the high-resolution spectrum, strongly indicating the
presence of a third star in the system, probably a rapidly rotating classical T
Tauri star. We incorporate this third light into our radial velocity and light
curve modeling of the eclipsing pair, measuring accurate masses (M_1 = 0.391
\pm 0.032, M_2 = 0.385 \pm 0.032 M\odot), radii (R_1 = 1.73 \pm 0.02, R_2 =
1.62 \pm 0.02 R\odot), and temperature ratio (T_1/T_2 = 1.0924 \pm 0.0017).
Thus the radii of the eclipsing stars differ by 6.9 \pm 0.8%, the temperatures
differ by 9.2 \pm 0.2%, and consequently the luminosities differ by 62 \pm 3%,
despite having masses equal to within 3%. This could be indicative of an age
difference of ~3x10^5 yr between the two eclipsing stars, perhaps a vestige of
the binary formation history. We find that the eclipsing pair is in an orbit
that has not yet fully circularized, e = 0.0166 \pm 0.003. In addition, we
measure the rotation rate of the eclipsing stars to be 4.629 \pm 0.006 d; they
rotate slightly faster than their 4.674 d orbit. The non-zero eccentricity and
super-synchronous rotation suggest that the eclipsing pair should be tidally
interacting, so we calculate the tidal history of the system according to
different tidal evolution theories. We find that tidal heating effects can
explain the observed luminosity difference of the eclipsing pair, providing an
alternative to the previously suggested age difference.Comment: 49 pages, 16 figures, 11 tables. Accepted for publication to Ap
Near-Infrared Light Curves of the Brown Dwarf Eclipsing Binary 2MASS J05352184-0546085: Can Spots Explain the Temperature Reversal?
We present the JHKs light curves for the double-lined eclipsing binary 2MASS
J05352184-0546085, in which both components are brown dwarfs. We analyze these
light curves with the published Ic-band light curve and radial velocities to
provide refined measurements of the system's physical parameters. The component
masses and radii are here determined with an accuracy of ~6.5% and ~1.5%,
respectively. We confirm the previous surprising finding that the primary brown
dwarf has a cooler effective temperature than its companion. Next, we perform a
detailed study of the variations in the out-of-eclipse phases of the light
curves to ascertain the properties of any inhomogeneities on the surfaces of
the brown dwarfs. Our analysis reveals two low-amplitude periodic signals, one
attributable to the rotation of the primary (with a period of 3.293+/-0.001 d)
and the other to that of the secondary (14.05+/-0.05 d). Finally, we explore
the effects on the derived physical parameters of the system when spots are
included in the modeling. The observed low-amplitude rotational modulations are
well fit by cool spots covering a small fraction of their surfaces. To mimic
the observed ~200 K suppression of the primary's temperature, our model
requires that the primary possess a very large spot coverage fraction of ~65%.
Altogether, a spot configuration in which the primary is heavily spotted while
the secondary is lightly spotted can explain the apparent temperature reversal
and can bring the temperatures of the brown dwarfs into agreement with the
predictions of theoretical models.Comment: Accepted for publication in The Astrophysical Journal; 13 pages, 8
figures, 6 tables. Updated parameter uncertaintie
- …