5,804 research outputs found
The center-to-limb variation across the Fraunhofer lines of HD 189733; Sampling the stellar spectrum using a transiting planet
The center-to-limb variation (CLV) describes the brightness of the stellar
disk as a function of the limb angle. Across strong absorption lines, the CLV
can vary quite significantly. We obtained a densely sampled time series of
high-resolution transit spectra of the active planet host star HD 189733 with
UVES. Using the passing planetary disk of the hot Jupiter HD 189733 b as a
probe, we study the CLV in the wings of the Ca II H and K and Na I D1 and D2
Fraunhofer lines, which are not strongly affected by activity-induced
variability. In agreement with model predictions, our analysis shows that the
wings of the studied Fraunhofer lines are limb brightened with respect to the
(quasi-)continuum. The strength of the CLV-induced effect can be on the same
order as signals found for hot Jupiter atmospheres. Therefore, a careful
treatment of the wavelength dependence of the stellar CLV in strong absorption
lines is highly relevant in the interpretation of planetary transit
spectroscopy.Comment: Accepted in A&
Time-resolved UVES observations of a stellar flare on the planet host HD 189733 during primary transit
HD 189733 is an exoplanetary system consisting of a transiting hot Jupiter
and an active K2V-type main sequence star. We aim to use VLT/UVES high
resolution echelle spectra to study a stellar flare. We have performed
simultaneous analyses of the temporal evolution in several chromospheric
stellar lines, namely, the Ca II H and K lines, Halpha, Hbeta, Hgamma, Hdelta,
Hepsilon, the Ca II infrared triplet line, and He I D3. Observations were
carried out with a time resolution of approximately 1 min for a duration of
four hours, including a complete planetary transit. We determine the energy
released during the flare in all studied chromospheric lines combined to be
about 8.7e31 erg, which puts this event at the upper end of flare energies
observed on the Sun. Our analysis does not reveal any significant delay of the
flare peak observed in the Balmer and Ca II H and K lines, although we find a
clear difference in the temporal evolution of these lines. The He I D3 shows
additional absorption possibly related to the flare event. Based on the flux
released in Ca II H and K lines during the flare, we estimate the soft X-ray
flux emission to be 7e30 erg. The observed flare can be ranked as a moderate
flare on a K-type star and confirms a rather high activity level of HD 189733
host star. The cores of the studied chromospheric lines demonstrate the same
behavior and let us study the flare evolution. We demonstrate that the activity
of an exoplanet host star can play an important role in the detection of
exoplanet atmospheres, since these are frequently discovered as an additional
absorption in the line cores. A possible star-planet interaction responsible
for a flare occurrence during a transit can neither be confirmed nor ruled out.Comment: 12 pages, 9 figures, accepted for publication in A&
A planetary eclipse map of CoRoT-2a. Comprehensive lightcurve modeling combining rotational-modulation and transits
We analyze the surface structure of the planet host star CoRoT-2a using a
consistent model for both the `global' (i.e., rotationally modulated)
lightcurve and the transit lightcurves, using data provided by the CoRoT
mission. Selecting a time interval covering two stellar rotations and six
transits of the planetary companion CoRoT-2b, we adopt a `strip' model of the
surface to reproduce the photometric modulation inside and outside the transits
simultaneously. Our reconstructions show that it is possible to achieve
appropriate fits for the entire sub-interval using a low-resolution surface
model with 36 strips. The surface reconstructions indicate that the brightness
on the eclipsed section of the stellar surface is (6 +/- 1) % lower than the
average brightness of the remaining surface. This result suggests a
concentration of stellar activity in a band around the stellar equator similar
to the behavior observed on the Sun.Comment: accepted by A&A on 12/09/200
New Facts About Factor-Demand Dynamics: Employment, Jobs, and Workers
We provide a unified discussion of the relations among flows of workers, changes in employment and changes in the number of jobs at the level of the firm. Using the only available set of data (a nationally representative sample of Dutch firms in 1988 and 1990) we discover that: 1) Nearly half of all hiring is by firms where employment is not growing; 2) Over half of all firing is by firms that are not contracting; 3) Most firing is by firms that are also hiring; 4) Flows of workers within firms are small compared to flows into and out of firms; and 5) Accounting for simultaneous creation and destruction of jobs within firms adds roughly 15 percent to estimates of economywide job creation and destruction. The results imply that macroeconomic fluctuations can have substantial effects beyond those indicated by net employment changes at the firm level, and that studies of dynamic factor demand must account for variations in gross flows of workers.
Planetary eclipse mapping of CoRoT-2a. Evolution, differential rotation, and spot migration
The lightcurve of CoRoT-2 shows substantial rotational modulation and
deformations of the planet's transit profiles caused by starspots. We
consistently model the entire lightcurve, including both rotational modulation
and transits, stretching over approximately 30 stellar rotations and 79
transits. The spot distribution and its evolution on the noneclipsed and
eclipsed surface sections are presented and analyzed, making use of the high
resolution achievable under the transit path.
We measure the average surface brightness on the eclipsed section to be
(5\pm1) % lower than on the noneclipsed section. Adopting a solar spot
contrast, the spot coverage on the entire surface reaches up to 19 % and a
maximum of almost 40 % on the eclipsed section. Features under the transit
path, i.e. close to the equator, rotate with a period close to 4.55 days.
Significantly higher rotation periods are found for features on the noneclipsed
section indicating a differential rotation of . Spotted
and unspotted regions in both surface sections concentrate on preferred
longitudes separated by roughly 180 deg.Comment: Paper accepted by A&A 17/02/2010. For a better resolution paper
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http://www.hs.uni-hamburg.de/EN/Ins/Per/Huber/index.htm
Religiosity and Sexual Risk Behaviors Among Latina Adolescents: Trends from 1995 to 2008
Purpose: The purpose of this study was to determine trends in the influence of religiosity on sexual activity of Latina adolescents in the United States from 1995 to 2008 and to determine if differences existed between the Mexican American and other Latina groups.
Methods: The sample comprised the subset of unmarried, 15–21-year-old (mean 17 years) Latina female respondents in the 1995 (n=267), 2002 (n=306), and 2006–2008 (n=400) National Survey of Family Growth (NSFG) datasets. Associations between religiosity (importance of religion and service attendance) and history of ever having sex, number of sex partners, and age of sexual debut were investigated.
Results: Less than one half of Latinas in 1995 (44%) and in 2006–2008 (44%) reported that religion was very important to them, whereas in 2002, 50% reported it was important. Only in 1995 did Latinas who viewed religion as very important have a significantly lower level of sexual initiation. In 1995 and in 2006–2008, Latinas who held religion as very important had significantly fewer partners. In all three cohorts, the higher religious importance group had higher virgin survival rates. Across cohorts, approximately one third of respondents reported frequent religious attendance. In all cohorts, frequent attenders were less likely to have had sex, had fewer partners, and had older age at sexual debut. The survival rate as virgins for Mexican origin Latinas was higher in 1995 and 2002 compared to non-Mexican Latinas but was almost the same in 2006–2008.
Conclusions: Religiosity had a protective association with sexual activity among Latina adolescents. The association of importance of religion with sexual activity has diminished from 1995 to 2008, however, whereas the importance of service attendance has remained stable. The influence of religion was more apparent among the Latinas of Mexican origin, but this greater influence also diminished by 2006–2008
Transition from a phase-segregated state to single-phase incommensurate sodium ordering in Na_xCoO_2 with x \approx 0.53
Synchrotron X-ray diffraction investigations of two single crystals of
Na_xCoO_2 from different batches with composition x = 0.525-0.530 reveal
homogeneous incommensurate sodium ordering with propagation vector (0.53 0.53
0) at room-temperature. The incommensurate (qq0) superstructure exists between
220 K and 430 K. The value of q varies between q = 0.514 and 0.529, showing a
broad plateau at the latter value between 260 K and 360 K. On cooling, unusual
reversible phase segregation into two volume fractions is observed. Below 220
K, one volume fraction shows the well-known commensurate orthorhombic x = 0.50
superstructure, while a second volume fraction with x = 0.55 exhibits another
commensurate superstructure, presumably with a 6a x 6a x c hexagonal supercell.
We argue that the commensurate-to-incommensurate transition is an intrinsic
feature of samples with Na concentrations x = 0.5 + d with d ~ 0.03.Comment: Corrected/improved versio
Disorder-induced Spin Gap in the Zigzag Spin-1/2 Chain Cuprate Sr_{0.9}Ca_{0.1}CuO_2
We report a comparative study of 63Cu Nuclear Magnetic Resonance spin lattice
relaxation rates, T_1^{-1}, on undoped SrCuO_2 and Ca doped
Sr_{0.9}Ca_{0.1}CuO_2 spin chain compounds. A temperature independent T_1^{-1}
is observed for SrCuO_2 as expected for an S=1/2 Heisenberg chain.
Surprisingly, we observe an exponential decrease of T_1^{-1} for T < 90,K in
the Ca-doped sample evidencing the opening of a spin gap. The data analysis
within the J_1-J_2 Heisenberg model employing density-matrix renormalization
group calculations suggests an impurity driven small alternation of the
J_2-exchange coupling as a possible cause of the spin gap.Comment: 4 pages, 4 figure
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