227 research outputs found
Geometry Diagnostics of a Stellar Flare from Fluorescent X-rays
We present evidence of Fe fluorescent emission in the Chandra HETGS spectrum
of the single G-type giant HR 9024 during a large flare. In analogy to solar
X-ray observations, we interpret the observed Fe K line as being
produced by illumination of the photosphere by ionizing coronal X-rays, in
which case, for a given Fe photospheric abundance, its intensity depends on the
height of the X-ray source. The HETGS observations, together with 3D Monte
Carlo calculations to model the fluorescence emission, are used to obtain a
direct geometric constraint on the scale height of the flaring coronal plasma.
We compute the Fe fluorescent emission induced by the emission of a single
flaring coronal loop which well reproduces the observed X-ray temporal and
spectral properties according to a detailed hydrodynamic modeling. The
predicted Fe fluorescent emission is in good agreement with the observed value
within observational uncertainties, pointing to a scale height \rstar. Comparison of the HR 9024 flare with that recently observed on II
Peg by Swift indicates the latter is consistent with excitation by X-ray
photoionization.Comment: accepted for publication on the Astrophysical Journal Letter
The HADES RV Programme with HARPS-N at TNG XI. GJ 685 b: a warm super-Earth around an active M dwarf
Small rocky planets seem to be very abundant around low-mass M-type stars.
Their actual planetary population is however not yet precisely understood.
Currently several surveys aim to expand the statistics with intensive detection
campaigns, both photometric and spectroscopic. We analyse 106 spectroscopic
HARPS-N observations of the active M0-type star GJ 685 taken over the past five
years. We combine these data with photometric measurements from different
observatories to accurately model the stellar rotation and disentangle its
signals from genuine Doppler planetary signals in the RV data. We run an MCMC
analysis on the RV and activity indexes time series to model the planetary and
stellar signals present in the data, applying Gaussian Process regression
technique to deal with the stellar activity signals. We identify three periodic
signals in the RV time series, with periods of 9, 24, and 18 d. Combining the
analyses of the photometry of the star with the activity indexes derived from
the HARPS-N spectra, we identify the 18 d and 9 d signals as activity-related,
corresponding to the stellar rotation period and its first harmonic
respectively. The 24 d signals shows no relations with any activity proxy, so
we identify it as a genuine planetary signal. We find the best-fit model
describing the Doppler signal of the newly-found planet, GJ 685\,b,
corresponding to an orbital period d and a
minimum mass M. We also study a
sample of 70 RV-detected M-dwarf planets, and present new statistical evidence
of a difference in mass distribution between the populations of single- and
multi-planet systems, which can shed new light on the formation mechanisms of
low-mass planets around late-type stars.Comment: 18 pages, 13 figures, accepted for publication in A&
HADES RV Programme with HARPS-N at TNG VI. GJ 3942 b behind dominant activity signals
Short- to mid-term magnetic phenomena on the stellar surface of M-type stars
cannot only resemble the effects of planets in radial velocity data, but also
may hide them. We analyze 145 spectroscopic HARPS-N observations of GJ 3942
taken over the past five years and additional photometry to disentangle stellar
activity effects from genuine Doppler signals as a result of the orbital motion
of the star around the common barycenter with its planet. To achieve this, we
use the common methods of pre-whitening, and treat the correlated red noise by
a first-order moving average term and by Gaussian-process regression following
an MCMC analysis. We identify the rotational period of the star at 16.3 days
and discover a new super-Earth, GJ 3942 b, with an orbital period of 6.9 days
and a minimum mass of 7.1 Me. An additional signal in the periodogram of the
residuals is present but we cannot claim it to be related to a second planet
with sufficient significance at this point. If confirmed, such planet candidate
would have a minimum mass of 6.3 Me and a period of 10.4 days, which might
indicate a 3:2 mean-motion resonance with the inner planet
HADES RV Programme with HARPS-N at TNG. VII. Rotation and activity of M-Dwarfs from time-series high-resolution spectroscopy of chromospheric indicators
We aim to investigate the presence of signatures of magnetic cycles and
rotation on a sample of 71 early M-dwarfs from the HADES RV programme using
high-resolution time-series spectroscopy of the Ca II H & K and Halpha
chromospheric activity indicators, the radial velocity series, the parameters
of the cross correlation function and the V-band photometry. We used mainly
HARPS-N spectra, acquired over four years, and add HARPS spectra from the
public ESO database and ASAS photometry light-curves as support data, extending
the baseline of the observations of some stars up to 12 years. We provide
log(R'hk) measurements for all the stars in the sample, cycle length
measurements for 13 stars, rotation periods for 33 stars and we are able to
measure the semi-amplitude of the radial velocity signal induced by rotation in
16 stars. We complement our work with previous results and confirm and refine
the previously reported relationships between the mean level of chromospheric
emission, measured by the log(R'hk), with the rotation period, and with the
measured semi-amplitude of the activity induced radial velocity signal for
early M-dwarfs. We searched for a possible relation between the measured
rotation periods and the lengths of the magnetic cycle, finding a weak
correlation between both quantities. Using previous v sin i measurements we
estimated the inclinations of the star's poles to the line of sight for all the
stars in the sample, and estimate the range of masses of the planets GJ 3998 b
and c (2.5 - 4.9 Mearth and 6.3 - 12.5 Mearth), GJ 625 b (2.82 Mearth), GJ 3942
b (7.1 - 10.0 Mearth) and GJ 15A b (3.1 - 3.3 Mearth), assuming their orbits
are coplanar with the stellar rotation.Comment: 19 pages, 16 figures, 10 table
The GAPS Programme with HARPS-N at TNG. X. Differential abundances in the XO-2 planet hosting binary
Binary stars hosting exoplanets are a unique laboratory where chemical
tagging can be performed to measure with high accuracy the elemental abundances
of both stellar components, with the aim to investigate the formation of
planets and their subsequent evolution. Here, we present a high-precision
differential abundance analysis of the XO-2 wide stellar binary based on high
resolution HARPS-N@TNG spectra. Both components are very similar K-dwarfs and
host planets. Since they formed presumably within the same molecular cloud, we
expect they should possess the same initial elemental abundances. We
investigate if the presence of planets can cause some chemical imprints in the
stellar atmospheric abundances. We measure abundances of 25 elements for both
stars with a range of condensation temperature K, achieving
typical precisions of dex. The North component shows abundances in
all elements higher by dex on average, with a mean
difference of +0.078 dex for elements with K. The
significance of the XO-2N abundance difference relative to XO-2S is at the
level for almost all elements. We discuss the possibility that this
result could be interpreted as the signature of the ingestion of material by
XO-2N or depletion in XO-2S due to locking of heavy elements by the planetary
companions. We estimate a mass of several tens of in heavy
elements. The difference in abundances between XO-2N and XO-2S shows a positive
correlation with the condensation temperatures of the elements, with a slope of
dex K, which could mean that both
components have not formed terrestrial planets, but that first experienced the
accretion of rocky core interior to the subsequent giant planets.Comment: 10 pages, 5 figures, accepted by Astronomy & Astrophysics. Numbering
of the series change
Gene Expression Differences between Enriched Normal and Chronic Myelogenous Leukemia Quiescent Stem/Progenitor Cells and Correlations with Biological Abnormalities
In comparing gene expression of normal and CML CD34+ quiescent (G0) cell, 292 genes were downregulated and 192 genes upregulated in the CML/G0 Cells. The differentially expressed genes were grouped according to their reported functions, and correlations were sought with biological differences previously observed between the same groups. The most relevant findings include the following. (i) CML G0 cells are in a more advanced stage of development and more poised to proliferate than normal G0 cells. (ii) When CML G0 cells are stimulated to proliferate, they differentiate and mature more rapidly than normal counterpart. (iii) Whereas normal G0 cells form only granulocyte/monocyte colonies when stimulated by cytokines, CML G0 cells form a combination of the above and erythroid clusters and colonies. (iv) Prominin-1 is the gene most downregulated in CML G0 cells, and this appears to be associated with the spontaneous formation of erythroid colonies by CML progenitors without EPO
The HADES RV Programme with HARPS-N@TNG II. Data treatment and simulations
The distribution of exoplanets around low-mass stars is still not well
understood. Such stars, however, present an excellent opportunity of reaching
down to the rocky and habitable planet domains. The number of current
detections used for statistical purposes is still quite modest and different
surveys, using both photometry and precise radial velocities, are searching for
planets around M dwarfs. Our HARPS-N red dwarf exoplanet survey is aimed at the
detection of new planets around a sample of 78 selected stars, together with
the subsequent characterization of their activity properties. Here we
investigate the survey performance and strategy. From 2700 observed spectra, we
compare the radial velocity determinations of the HARPS-N DRS pipeline and the
HARPS-TERRA code, we calculate the mean activity jitter level, we evaluate the
planet detection expectations, and we address the general question of how to
define the strategy of spectroscopic surveys in order to be most efficient in
the detection of planets. We find that the HARPS-TERRA radial velocities show
less scatter and we calculate a mean activity jitter of 2.3 m/s for our sample.
For a general radial velocity survey with limited observing time, the number of
observations per star is key for the detection efficiency. In the case of an
early M-type target sample, we conclude that approximately 50 observations per
star with exposure times of 900 s and precisions of about 1 m/s maximizes the
number of planet detections
The HADES RV Programme with HARPS-N@TNG IV. Time resolved analysis of the Ca ii H&K and H{\alpha} chromospheric emission of low-activity early-type M dwarfs
M dwarfs are prime targets for planet search programs, particularly of those
focused on the detection and characterization of rocky planets in the habitable
zone. Understanding their magnetic activity is important because it affects our
ability to detect small planets, and it plays a key role in the
characterization of the stellar environment. We analyze observations of the Ca
II H&K and H{\alpha} lines as diagnostics of chromospheric activity for
low-activity early-type M dwarfs. We analyze the time series of spectra of 71
early-type M dwarfs collected for the HADES project for planet search purposes.
The HARPS-N spectra provide simultaneously the H&K doublet and the H{\alpha}
line. We develop a reduction scheme able to correct the HARPS-N spectra for
instrumental and atmospheric effects, and to provide flux-calibrated spectra in
units of flux at the stellar surface. The H&K and H{\alpha} fluxes are compared
with each other, and their variability is analyzed. We find that the H and K
flux excesses are strongly correlated with each other, while the H{\alpha} flux
excess is generally less correlated with the H&K doublet. We also find that
H{\alpha} emission does not increase monotonically with the H&K line flux,
showing some absorption before being filled in by chromospheric emission when
H&K activity increases. Analyzing the time variability of the emission fluxes,
we derive a tentative estimate of the rotation period (of the order of a few
tens of days) for some of the program stars, and the typical lifetime of
chromospheric active regions (a few stellar rotations). Our results are in good
agreement with previous studies. In particular, we find evidence that the
chromospheres of early-type M dwarfs could be characterized by different
filaments coverage, affecting the formation mechanism of the H{\alpha} line. We
also show that chromospheric structure is likely related to spectral type
The GAPS Programme with HARPS-N at TNG XV. A substellar companion around a K giant star identified with quasi-simultaneous HARPS-N and GIANO measurements
Context. Identification of planetary companions of giant stars is made
difficult because of the astrophysical noise, that may produce radial velocity
(RV) variations similar to those induced by a companion. On the other hand any
stellar signal is wavelength dependent, while signals due to a companion are
achromatic. Aims. Our goal is to determine the origin of the Doppler periodic
variations observed in the thick disk K giant star TYC 4282-605-1 by HARPS-N at
the Telescopio Nazionale Galileo (TNG) and verify if they can be due to the
presence of a substellar companion. Methods. Several methods have been used to
exclude the stellar origin of the observed signal including detailed analysis
of activity indicators and bisector and the analysis of the photometric light
curve. Finally we have conducted an observational campaign to monitor the near
infrared (NIR) RV with GIANO at the TNG in order to verify whether the NIR
amplitude variations are comparable with those observed in the visible.
Results. Both optical and NIR RVs show consistent variations with a period at
101 days and similar amplitude, pointing to the presence of a companion
orbiting the target. The main orbital properties obtained for our giant star
with a derived mass of M=0.97+-0.03M_sun are
M_Psini=10.78+-0.12MJ;P=101.54+-0.05days;e=0.28+-0.01 and a=0.422+-0.009AU. The
chemical analysis shows a significant enrichment in the abundance of Nai, Mgi,
Ali and S i while the rest of analyzed elements are consistent with the solar
value demonstrating that the chemical composition corresponds with an old K
giant (age = 10.1 Gyr) belonging to local thick disk. Conclusions. We conclude
that the substellar companion hypothesis for this K giant is the best
explanation for the observed periodic RV variation. This study also shows the
high potential of multi-wavelength RV observations for the validation of planet
candidates.Comment: Accepted in Journal reference A&A 14/06/201
The GAPS Programme with HARPS-N@TNG XIV. Investigating giant planet migration history via improved eccentricity and mass determination for 231 transiting planets
We carried out a Bayesian homogeneous determination of the orbital parameters
of 231 transiting giant planets (TGPs) that are alone or have distant
companions; we employed DE-MCMC methods to analyse radial-velocity (RV) data
from the literature and 782 new high-accuracy RVs obtained with the HARPS-N
spectrograph for 45 systems over 3 years. Our work yields the largest sample of
systems with a transiting giant exoplanet and coherently determined orbital,
planetary, and stellar parameters. We found that the orbital parameters of TGPs
in non-compact planetary systems are clearly shaped by tides raised by their
host stars. Indeed, the most eccentric planets have relatively large orbital
separations and/or high mass ratios, as expected from the equilibrium tide
theory. This feature would be the outcome of high-eccentricity migration (HEM).
The distribution of , where and are the semi-major axis
and the Roche limit, for well-determined circular orbits peaks at 2.5; this
also agrees with expectations from the HEM. The few planets of our sample with
circular orbits and values may have migrated through disc-planet
interactions instead of HEM. By comparing circularisation times with stellar
ages, we found that hot Jupiters with au have modified tidal quality
factors are
required to explain the presence of eccentric planets at the same orbital
distance. As a by-product of our analysis, we detected a non-zero eccentricity
for HAT-P-29; we determined that five planets that were previously regarded to
have hints of non-zero eccentricity have circular orbits or undetermined
eccentricities; we unveiled curvatures caused by distant companions in the RV
time series of HAT-P-2, HAT-P-22, and HAT-P-29; and we revised the planetary
parameters of CoRoT-1b.Comment: 44 pages (16 pages of main text and figures), 11 figures, 5
longtables, published in Astronomy and Astrophysics, Volume 602, A107 (2017).
Tables with new HARPS-N and TRES radial-velocity data (Tables 1 and 2),
stellar parameters (Table 7), orbital parameters and RV jitter (Table 8), and
planet physical parameters (Table 9) are available as ancillary files
(sidebar on the right
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