Context. The sudden optical brightening of two young stellar objects, HBC 722 and VSX J205126.1+440523, located in the North America/Pelican Nebula Complex, was announced in August 2010. Early photometric and spectroscopic observations of these objects indicated that they may belong to the FUor or EXor class of young eruptive stars. The eruptions of FUors and EXors are often explained by enhanced accretion of material from the circumstellar disk to the protostar. Aims. In order to determine the true nature of these two objects, we started an optical and near-infrared monitoring program, and complemented our data with archival observations and data from the literature.Methods. We plot and analyze pre-outburst and outburst spectral energy distributions (SEDs), multi-filter light curves, and colorcolor diagrams. Results. The quiescent SED of HBC 722 is consistent with that of a slightly reddened normal T Tauri-type star. The source brightened monotonically in about two months, and the SED obtained during maximum brightness indicates the appearance of a hot, singletemperature blackbody. The current fading rate implies that the star will return to quiescence in about a year, which questions its classification as a bone fide FUor. The quiescent SED of VSX J205126.1+440523 looks like that of a highly embedded Class I source. The outburst of this source happened more gradually, but reached an unprecedentedly high amplitude. Its light curves showed a deep minimum two and a half months after the peak, when the object was close to its pre-outburst optical brightness. Further monitoring indicates that it is still far from being quiescent. Conclusions. The shape of the light curves as well as the bolometric luminosities and accretion rates suggest that these objects do not fit into the classic FUor group. Although HBC 722 exhibits all spectral characteristics of a bona fide FUor, its luminosity and accretion rate is too low and its timescale is too fast compared with classical FUors. VSX J205126.1+440523 seems to be an example where quick extinction changes modulate the light curve.
The fitting of radial velocity curves is a frequent procedure in binary stars and exoplanet research. In the majority of cases the fitting routines need to be fed with a set of initial parameter values and priors from which to begin the computations and their results can be affected by local minima. We present a new code, the rvfit code, for fitting radial velocities of stellar binaries and exoplanets using an Adaptive Simulated Annealing (ASA) global minimization method, which fastly converges to a global solution minimum without the need to provide preliminary parameter values. We show the performance of the code using both synthetic and real data sets: double-lined binaries, single-lined binaries, and exoplanet systems. In all examples the keplerian orbital parameters fitted by the rvfit code and their computed uncertainties are compared with literature solutions. Finally, we provide the source code with a working example and a detailed description on how to use it.
Context. V2492 Cyg is a young eruptive star that went into outburst in 2010. The near-infrared color changes observed since the outburst peak suggest that the source belongs to a newly defined sub-class of young eruptive stars, where time-dependent accretion and variable line-of-sight extinction play a combined role in the flux changes. Aims. In order to learn about the origin of the light variations and to explore the circumstellar and interstellar environment of V2492 Cyg, we monitored the source at ten different wavelengths, between 0.55 μm and 2.2 μm from the ground and between 3.6 μm and 160 μm from space. Methods. We analyze the light curves and study the color−color diagrams via comparison with the standard reddening path. We examine the structure of the molecular cloud hosting V2492 Cyg by computing temperature and optical depth maps from the far-infrared data. Results. We find that the shapes of the light curves at different wavelengths are strictly self-similar and that the observed variability is related to a single physical process, most likely variable extinction. We suggest that the central source is episodically occulted by a dense dust cloud in the inner disk and, based on the invariability of the far-infrared fluxes, we propose that it is a long-lived rather than a transient structure. In some respects, V2492 Cyg can be regarded as a young, embedded analog of UX Orionis-type stars. Conclusions. The example of V2492 Cyg demonstrates that the light variations of young eruptive stars are not exclusively related to changing accretion. The variability provided information on an azimuthally asymmetric structural element in the inner disk. Such an asymmetric density distribution in the terrestrial zone may also have consequences for the initial conditions of planet formation.
In Morales et al. (2009), we have recently investigated the mid-infrared (3.6 to 8.0 micron) variability of young-stellar objects (YSOs) using the IRAC camera on the Spitzer Space Telescope. Specifically, we obtained synoptic photometry of about 70 YSOs in the ∼1 Myr old IC1396A globule over a 14 day period. More than half of the YSOs were detectably variable, with amplitudes up to about 0.2 magnitudes. About a third of these objects showed quasi-sinusoidal light curves with apparent periods of typically 5 to 12 days. At least two families of models can explain such light curves: (a) a Class II YSO with a photospheric hot spot which locally heats the inner circumstellar disk which is viewed from slightly above the disk plane, and (b) a YSO with a warped disk or with some other non-axisymmetric inner disk density profile, also seen with a view angle slightly above the disk plane. The two models can both yield light curve shapes and amplitudes similar to what we observe in the mid-infrared, but produce very different light curves at shorter wavelengths dominated by the stellar photosphere. Because we only had IRAC photometry for IC1396A, we were not able to discriminate between the two models for this set of data.We have just begun a much more extensive monitoring program to obtain synoptic observations of >1500 YSOs in Orion and eleven other star formation regions. The new effort -called YSOVAR -is a Spitzer "Warm Mission Exploration Science" program allocated 550 hours of observing time. For each cluster, we will obtain about 100 epochs of IRAC photometry, normally mostly in a 40 day window of time. We will also obtain a large body of optical and near-IR photometry in order to discriminate between the different physical models. Observations of IC1396A and the inner one square degree of the Orion Nebula Cluster will be obtained during Sept.-Dec. 2009. All of the IRAC data from the program will be made publicly available within 90 days of their being pipeline processed. The optical and near-IR photomtry will also be made public, as rapidly as we can do so.Details about YSOVAR, the clusters to be observed, and the schedule of observations can be found at http://ysovar.ipac.caltech.edu/.
Introducción: Se realizó una comparación del estado nutricional, hábitos alimentarios, actividad física y horas de sueño en estudiantes de 5° a 8° grado de educación primaria en una escuela pública de la ciudad Punta Arenas Chile, según las estaciones de invierno y verano considerando la variabilidad climática y de luz solar de un clima extremo.Material y métodos: Estudio observacional analítico de enfoque cuantitativo, longitudinal de cohorte. Se siguieron durante un período de 7 meses a 105 estudiantes de ambos sexos cuya edad promedio fue 11,5 años. Se realizaron dos mediciones de las cuatro variables en estudio (estado nutricional, hábitos alimentarios, actividad física y horas de sueño). Se efectuaron mediciones de peso y talla para la obtención del Índice de Masa Corporal (IMC) para clasificar el estado nutricional según IMC/edad con los patrones de crecimiento recomendados por la Organización Mundial de la Salud (OMS). Los hábitos alimentarios y sueño fueron evaluados con un cuestionario auto administrado y se categorizó las horas de sueño para la edad según National Sleep Foundation. Para la evaluación de la actividad física en los estudiantes se utilizó la Physical Activity Questionnaire for Children PAQ-C. El análisis de datos se realizó con el Software estadístico SPSSⓇ Versión 22 y la prueba estadística t-student para muestras relacionadas. Resultados: No se encontró diferencia significativa en el estado nutricional (p 0,57). Los hábitos alimentarios saludables y la actividad física disminuyen en la estación de verano (p> 0,05). Las horas de sueño no tuvieron diferencias significativas en ambas estaciones con un promedio de 8,3 horas. Conclusiones: Los hábitos alimentarios saludables y de actividad física disminuyen en la estación de verano posiblemente asociados al receso escolar, sin evidenciar un efecto directo de la estación de año sobre las variables estudiadas.
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