339 research outputs found
Strong HI Lyman- variations from the 11 Gyr-old host star Kepler-444: a planetary origin ?
Kepler-444 provides a unique opportunity to probe the atmospheric composition
and evolution of a compact system of exoplanets smaller than the Earth. Five
planets transit this bright K star at close orbital distances, but they are too
small for their putative lower atmosphere to be probed at optical/infrared
wavelengths. We used the Space Telescope Imaging Spectrograph instrument
onboard the Hubble Space Telescope to search for the signature of the planet's
upper atmospheres at six independent epochs in the Ly- line. We detect
significant flux variations during the transits of both Kepler-444e and f
(~20%), and also at a time when none of the known planets was transiting
(~40%). Variability in the transition region and corona of the host star might
be the source of these variations. Yet, their amplitude over short time scales
(~2-3 hours) is surprisingly strong for this old (11.2+-1.0Gyr) and apparently
quiet main-sequence star. Alternatively, we show that the in-transits
variations could be explained by absorption from neutral hydrogen exospheres
trailing the two outer planets (Kepler-444e and f). They would have to contain
substantial amounts of water to replenish such hydrogen exospheres, which would
reveal them as the first confirmed ocean-planets. The out-of-transit
variations, however, would require the presence of a yet-undetected Kepler-444g
at larger orbital distance, casting doubt on the planetary origin scenario.
Using HARPS-N observations in the sodium doublet, we derived the properties of
two Interstellar Medium clouds along the line-of-sight toward Kepler-444. This
allowed us to reconstruct the stellar Ly- line profile and to estimate
the XUV irradiation from the star, which would still allow for a moderate mass
loss from the outer planets after 11.2Gyr. Follow-up of the system at XUV
wavelengths will be required to assess this tantalizing possibility.Comment: Accepted for publication in A&A Name of the system added to the title
in most recent versio
Quiescent and active phases in Be stars : A WISE snapshot of Young Galactic Open Clusters
Through the modeling of near-infrared photometry of star-plus disk systems with the codes bedisk/beray, we successfully describe the Wide-Field Infrared Survey Explorer (WISE) photometric characteristics of Be stars in five young open clusters, NGC 663, NGC 869, NGC 884, NGC 3766, and NGC 4755, broadly studied in the literature. WISE photometry allows previously known Be stars to be detected and to find new Be candidates which could be confirmed spectroscopically. The location of Be stars in the WISE color-magnitude diagram, separates them in two groups; active (Be stars hosting a developed circumstellar disk) and quiescent objects (Be stars in a diskless phase), and this way, we can explore how often stars are observed in these different stages. The variability observed in most active variable Be stars is compatible with a disk dissipation phase. We find that 50% of Be stars in the studied open clusters are in an active phase. We can interpret this as Be stars having a developed circumstellar disk one-half of the time. The location of Be stars with a developed disk in the color-magnitude diagram require mass loss rates in agreement with values recently reported in the literature. For these objects, we expect to have a tight relation between the equivalent width of the Hα line and the mass of the disk, if the inclination is known. Also, near-infrared photometry of Be stars in stellar clusters has the potential of being useful to test whether there is a preferential viewing angle.Instituto de Astrofísica de La Plat
Hybrid media consumption: How tweeting during a televised political debate influences the vote decision
An increasing number of people are using microblogs to broadcast their thoughts in real time as they watch televised political events. Microblogging social network sites (SNSs)
such as Twitter generate a parallel stream of information and opinion. It is presumed that the additional content enhances the viewing experience, but our experiment explores the validity of this assumption. We studied how tweeting, or passively observing Twitter during a debate, influenced affect, recall and vote decision. For most measures, participants’ average feeling and recall toward the candidates did not depend on Twitter activity, but Twitter activity did matter for vote choice. People who actively tweeted changed their voting choice to reflect the majority sentiment on Twitter. Results are discussed in terms of the possibility that active tweeting leads to greater engagement but that it may also make people more susceptible to social influence
Critical study of the distribution of rotational velocities of Be stars; II: Differential rotation and some hidden effects interfering with the interpretation of the Vsin i parameter
We assume that stars may undergo surface differential rotation to study its
impact on the interpretation of and on the observed distribution
of ratios of true rotational velocities u=V/V_\rm c (V_\rm c is
the equatorial critical velocity). We discuss some phenomena affecting the
formation of spectral lines and their broadening, which can obliterate the
information carried by concerning the actual stellar rotation. We
studied the line broadening produced by several differential rotational laws,
but adopted Maunder's expression
as an attempt to account for
all of these laws with the lowest possible number of free parameters. We
studied the effect of the differential rotation parameter on the
measured parameter and on the distribution of ratios
u=V/V_\rm c. We conclude that the inferred is smaller than
implied by the actual equatorial linear rotation velocity V_\rm eq if the
stars rotate with . For a
given the deviations of are larger when . If
the studied Be stars have on average , the number of rotators with
V_\rm eq\simeq0.9V_\rm c is larger than expected from the observed
distribution ; if these stars have on average , this number
is lower than expected. We discuss seven phenomena that contribute either to
narrow or broaden spectral lines, which blur the information on the rotation
carried by and, in particular, to decide whether the Be phenomenon
mostly rely on the critical rotation. We show that two-dimensional radiation
transfer calculations are needed in rapid rotators to diagnose the stellar
rotation more reliably.Comment: To appear in A&
Promoter hypermethylation of SHOX2 and SEPT9 is a potential biomarker for minimally invasive diagnosis in adenocarcinomas of the biliary tract
Clinicopathological data of the 20 biliary tract cancer cases and 100 gender- and age-matched controls included in plasma study. (XLSX 116 kb
Be Stars: Rapidly Rotating Pulsators
I will show that Be stars are, without exception, a class of rapidly rotating
stars, which are in the majority of cases pulsating stars as well, while none
of them does possess a large scale (i.e. with significant dipolar contribution)
magnetic field.Comment: Review talk given at "XX Stellar Pulsation Conference Series: Impact
of new instrumentation and new insights in stellar pulsations", Granada, 5-9
September 2011, in press in AIP Conf. Se
Identification of a novel class of autotaxin inhibitors through cross-screening
Three novel series were generated in order to mimic the pharmacophoric features displayed by lead compound AM095, a Lysophosphatidic acid (LPA1) receptor antagonist. Biological evaluation of this array of putative LPA1 antagonists led us to the discovery of three novel series of inhibitors of the ecto-enzyme Autotaxin (ATX), responsible for LPA production in blood, with potencies in the range 1 – 4 μM accompanied with good (> 100 μg/mL) solubility
Lack of functional GABA receptors alters Kiss1 , Gnrh1 and Gad1 mRNA expression in the medial basal hypothalamus at postnatal day 4
Background/Aims: Adult mice lacking functional GABAB receptors (GABAB1KO) show altered Gnrh1 and Gad1 expressions in the preoptic area-anterior hypothalamus (POA-AH) and females display disruption of cyclicity and fertility. Here we addressed whether sexual differentiation of the brain and the proper wiring of the GnRH and kisspeptin systems were already disturbed in postnatal day 4 (PND4) GABAB1KO mice. Methods: PND4 wild-type (WT) and GABAB1KO mice of both sexes were sacrificed; tissues were collected to determine mRNA expression (qPCR), amino acids (HPLC), and hormones (RIA and/or IHC). Results: GnRH neuron number (IHC) did not differ among groups in olfactory bulbs or OVLT-POA. Gnrh1 mRNA (qPCR) in POA-AH was similar among groups. Gnrh1 mRNA in medial basal hypothalamus (MBH) was similar in WTs but was increased in GABAB1KO females compared to GABAB1KO males. Hypothalamic GnRH (RIA) was sexually different in WTs (males < females), but this sex difference was lost in GABAB1KOs; the same pattern was observed when analyzing only the MBH, but not in the POA-AH. Arcuate nucleus Kiss1 mRNA (micropunch-qPCR) was higher in WT females than in WT males and GABAB1KO females. Gad1 mRNA in MBH was increased in GABAB1KO females compared to GABAB1KO males. Serum LH and gonadal estradiol content were also increased in GABAB1KOs. Conclusion: We demonstrate that GABABRs participate in the sexual differentiation of the ARC/MBH, because sex differences in several reproductive genes, such as Gad1, Kiss1 and Gnrh1, are critically disturbed in GABAB1KO mice at PND4, probably altering the organization and development of neural circuits governing the reproductive axis. (c) 2013 S. Karger AG, Basel
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