150 research outputs found
Time evolution and rotation of starspots on CoRoT-2 from the modelling of transit photometry
CoRoT-2, the second planet-hosting star discovered by the CoRoT satellite, is
a young and active star. A total of 77 transits were observed for this system
over a period of 135 days. Small modulations detected in the optical light
curve of the planetary transits are used to study the position, size,
intensity, and temporal evolution of the photospheric spots on the surface of
the star that are occulted by the planetary disk. We apply a spot model to
these variations and create a spot map of the stellar surface of CoRoT-2 within
the transit band for every transit. From these maps, we estimate the stellar
rotation period and obtain the longitudes of the spots in a reference frame
rotating with the star. Moreover, the spots temporal evolution is determined.
This model achieves a spatial resolution of 2\circ. Mapping of 392 spots vs.
longitude indicates the presence of a region free of spots, close to the
equator, reminiscent of the coronal holes observed on the Sun during periods of
maximum activity. With this interpretation, the stellar rotation period within
the transit latitudes of -14.\circ 6 \pm 10 \circ is found to be 4.48 days.
This rotation period is shorter than the 4.54 days as derived from the
out-of-transit light modulation. Since the transit data samples a region close
to the stellar equator, while the period determined from out-of-transit data
reflects the average rotation of the star, this is taken as an indication of a
latitudinal differential rotation of about 3% or 0.042 rad/d.Comment: 8 pages, 12 figure
Properties of starspots on CoRoT-2
As a planet eclipses its parent star, a dark spot on the surface of the star
may be occulted, causing a detectable variation in the light curve. A total of
77 consecutive transit light curves of CoRoT-2 were observed with a high
temporal resolution of 32 s, corresponding to an uninterrupted period of 134
days. By analyzing small intensity variations in the transit light curves, it
was possible to detect and characterize spots at fixed positions (latitude and
longitude) on the surface of the star. The model used simulates planetary
transits and enables the inclusion of spots on the stellar surface with
different sizes, intensities (i.e. temperatures), and positions. Fitting the
data by this model, it is possible to infer the spots physical characteristics.
The fits were either in spot longitude and radius, with a fixed intensity, or
in spots longitude and intensity, for spots of constant size. Before the
modeling of the spots were performed, the planetary radius relative to the star
radius was estimated by fitting the deepest transit to minimize the effect of
spots. A slightly larger (3%) radius, 0.172 Rstar, resulted instead of the
previously reported 0.1667 Rstar . The fitting of the transits yield spots, or
spot groups, with sizes of ranging from 0.2 to 0.7 planet radius, Rp, with a
mean of (0.41 +/- 0.13) Rp (~100,000 km), resulting in a stellar area covered
by spots within the transit latitudes of 10-20%. The intensity varied from 0.4
to 0.9 of the disk center intensity, Ic, with a mean of (0.60 +/- 0.19) Ic,
which can be converted to temperature by assuming an effective temperature of
5625 K for the stellar photosphere, the spots temperature ranges mainly from
3600 to 5000 K. The results from the spot modeling are in agreement with those
found for magnetic activity analysis from out of transit data of the same star.Comment: 7 pages, 11 figure
Differential rotation of Kepler-71 via transit photometry mapping of faculae and starspots
Knowledge of dynamo evolution in solar-type stars is limited by the difficulty of using active region monitoring to measure stellar differential rotation, a key probe of stellar dynamo physics. This paper addresses the problem by presenting the first ever measurement of stellar differential rotation for a main-sequence solar-type star using starspots and faculae to provide complementary information. Our analysis uses modelling of light curves of multiple exoplanet transits for the young solar-type star Kepler-71, utilizing archival data from the Kepler mission. We estimate the physical characteristics of starspots and faculae on Kepler-71 from the characteristic amplitude variations they produce in the transit light curves and measure differential rotation from derived longitudes. Despite the higher contrast of faculae than those in the Sun, the bright features on Kepler-71 have similar properties such as increasing contrast towards the limb and larger sizes than sunspots. Adopting a solar-type differential rotation profile (faster rotation at the equator than the poles), the results from both starspot and facula analysis indicate a rotational shear less than about 0.005 rad d-1, or a relative differential rotation less than 2 per cent, and hence almost rigid rotation. This rotational shear contrasts with the strong rotational shear of zero-age main-sequence stars and the modest but significant shear of the modern-day Sun. Various explanations for the likely rigid rotation are considered
InfluĆŖncia de reguladores de crescimento e adubaĆ§Ć£o no florescimento e crescimento de Eucalyptus dunnii Maid.
A influĆŖncia de reguladores de crescimento e da adubaĆ§Ć£o sobre o florescimento e crescimento de Eucalyptus dunnii Maid., de cinco anos de idade, foi determinada em Ć”rvores selecionadas de um talhĆ£o experimental localizado no Centro Nacional de Pesquisa de Florestas/EMBRAPA, PR. Neste, foram realizadas aplicaƧƵes de Ć”cido giberĆ©lico (GA3) na concentraĆ§Ć£o de 300 mg. l -1 , cinetina a 50 mg. l -1 , combinaĆ§Ć£o das concentraƧƵes de GA3 + cinetina, Ethrel a 240 mg. l -1 e 400 g de 10-30-15 (NPK) mais 10 g de micronutrientes. O florescimento nĆ£o foi influenciado pelos tratamentos empregados. Entretanto, para o crescimento, verificou-se que os maiores incrementos para altura e diĆ¢metro foram obtidos com a aplicaĆ§Ć£o de GA3 + cinetina. A cinetina, isoladamente, teve um efeito negativo, enquanto que a adubaĆ§Ć£o nĆ£o trouxe acrĆ©scimo significativo no crescimento de E. dunnii. Com base nesses resultados, sugere-se que estudos posteriores, envolvendo outros tratamentos, sejam realizados para o estabelecimento da tĆ©cnica de induĆ§Ć£o do florescimento nessa espĆ©cie
Association of radio polar cap brightening with bright patches and coronal holes
Radio-bright regions near the solar poles are frequently observed in Nobeyama
Radioheliograph (NoRH) maps at 17 GHz, and often in association with coronal
holes. However, the origin of these polar brightening has not been established
yet. We propose that small magnetic loops are the source of these bright
patches, and present modeling results that reproduce the main observational
characteristics of the polar brightening within coronal holes at 17 GHz. The
simulations were carried out by calculating the radio emission of the small
loops, with several temperature and density profiles, within a 2D coronal hole
atmospheric model. If located at high latitudes, the size of the simulated
bright patches are much smaller than the beam size and they present the
instrument beam size when observed. The larger bright patches can be generated
by a great number of small magnetic loops unresolved by the NoRH beam. Loop
models that reproduce bright patches contain denser and hotter plasma near the
upper chromosphere and lower corona. On the other hand, loops with increased
plasma density and temperature only in the corona do not contribute to the
emission at 17 GHz. This could explain the absence of a one-to-one association
between the 17 GHz bright patches and those observed in extreme ultraviolet.
Moreover, the emission arising from small magnetic loops located close to the
limb may merge with the usual limb brightening profile, increasing its
brightness temperature and width.Comment: 8 pages, 6 figures, 1 table. Accepted for publication in The
Astrophysical Journa
Stellar activity and rotation of the planet host Kepler-17 from long-term space-borne photometry
The study of young Sun-like stars is of fundamental importance to understand
the magnetic activity and rotational evolution of the Sun. Space-borne
photometry by the Kepler telescope provides unprecedented datasets to
investigate these phenomena in Sun-like stars. We present a new analysis of the
entire Kepler photometric time series of the moderately young Sun-like star
Kepler-17 that is accompanied by a transiting hot Jupiter. We applied a
maximum-entropy spot model to the long-cadence out-of-transit photometry of the
target to derive maps of the starspot filling factor versus the longitude and
the time. These maps are compared to the spots occulted during transits to
validate our reconstruction and derive information on the latitudes of the
starspots. We find two main active longitudes on the photosphere of Kepler-17,
one of which has a lifetime of at least days, although with a
varying level of activity. The latitudinal differential rotation is of solar
type, that is, with the equator rotating faster than the poles. We estimate a
minimum relative amplitude between
and , our determination being affected by the finite lifetime of
individual starspots and depending on the adopted spot model parameters. We
find marginal evidence of a short-term intermittent activity cycle of
days and an indication of a longer cycle of days characterized by an
equatorward migration of the mean latitude of the spots as in the Sun. The
rotation of Kepler-17 is likely to be significantly affected by the tides
raised by its massive close-by planet. We confirm the reliability of
maximum-entropy spot models to map starspots in young active stars and
characterize the activity and differential rotation of this young Sun-like
planetary host.Comment: Accepted by Astronomy and Astrophysics - 22 pages, 29 figure, 1
table, 2 appendixe
Photospheric activity, rotation, and star-planet interaction of the planet-hosting star CoRoT-6
The CoRoT satellite has recently discovered a hot Jupiter that transits
across the disc of a F9V star called CoRoT-6 with a period of 8.886 days. We
model the photospheric activity of the star and use the maps of the active
regions to study stellar differential rotation and the star-planet interaction.
We apply a maximum entropy spot model to fit the optical modulation as observed
by CoRoT during a uninterrupted interval of about 140 days. Photospheric active
regions are assumed to consist of spots and faculae in a fixed proportion with
solar-like contrasts. Individual active regions have lifetimes up to 30-40
days. Most of them form and decay within five active longitudes whose different
migration rates are attributed to the stellar differential rotation for which a
lower limit of \Delta \Omega / \Omega = 0.12 \pm 0.02 is obtained. Several
active regions show a maximum of activity at a longitude lagging the
subplanetary point by about 200 degrees with the probability of a chance
occurrence being smaller than 1 percent. Our spot modelling indicates that the
photospheric activity of CoRoT-6 could be partially modulated by some kind of
star-planet magnetic interaction, while an interaction related to tides is
highly unlikely because of the weakness of the tidal force.Comment: 9 pages, 7 figures, accepted to Astronomy & Astrophysic
A Tentative Detection of a Starspot During Consecutive Transits of an Extrasolar Planet from the Ground: No Evidence of a Double Transiting Planet System Around TrES-1
There have been numerous reports of anomalies during transits of the planet
TrES-1b. Recently, Rabus and coworkers' analysis of HST observations lead them
to claim brightening anomalies during transit might be caused by either a
second transiting planet or a cool starspot. Observations of two consecutive
transits are presented here from the University of Arizona's 61-inch Kuiper
Telescope on May 12 and May 15, 2008 UT. A 5.4 +/- 1.7 mmag (0.54 +/- 0.17%)
brightening anomaly was detected during the first half of the transit on May 12
and again in the second half of the transit on May 15th. We conclude that this
is a tentative detection of a r greater than or equal to 6 earth radii starspot
rotating on the surface of the star. We suggest that all evidence to date
suggest TrES-1 has a spotty surface and there is no need to introduce a second
transiting planet in this system to explain these anomalies. We are only able
to constrain the rotational period of the star to 40.2 +22.9 -14.6 days, due to
previous errors in measuring the alignment of the stellar spin axis with the
planetary orbital axis. This is consistent with the previously observed P_obs =
33.2 +22.3 -14.3 day period. We note that this technique could be applied to
other transiting systems for which starspots exist on the star in the transit
path of the planet in order to constrain the rotation rate of the star.
(abridged)Comment: 21 pages, 3 tables, 6 figures, Accepted to Ap
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