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Register a new userNear-Infrared Light Curves of the Brown Dwarf Eclipsing Binary 2MASS J05352184-0546085: Can Spots Explain the Temperature Reversal?
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Yilen G\\'omez Maqueo Chew
Publication date
2009
fields
Physics
and research's language is
English
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We present the JHKs light curves for the double-lined eclipsing binary 2MASS J05352184-0546085, in which both components are brown dwarfs. We analyze these light curves with the published Ic-band light curve and radial velocities to provide refined measurements of the systems physical parameters. The component masses and radii are here determined with an accuracy of ~6.5% and ~1.5%, respectively. We confirm the previous surprising finding that the primary brown dwarf has a cooler effective temperature than its companion. Next, we perform a detailed study of the variations in the out-of-eclipse phases of the light curves to ascertain the properties of any inhomogeneities on the surfaces of the brown dwarfs. Our analysis reveals two low-amplitude periodic signals, one attributable to the rotation of the primary (with a period of 3.293+/-0.001 d) and the other to that of the secondary (14.05+/-0.05 d). Finally, we explore the effects on the derived physical parameters of the system when spots are included in the modeling. The observed low-amplitude rotational modulations are well fit by cool spots covering a small fraction of their surfaces. To mimic the observed ~200 K suppression of the primarys temperature, our model requires that the primary possess a very large spot coverage fraction of ~65%. Altogether, a spot configuration in which the primary is heavily spotted while the secondary is lightly spotted can explain the apparent temperature reversal and can bring the temperatures of the brown dwarfs into agreement with the predictions of theoretical models.
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We show high resolution spectra of the eclipsing brown dwarf binary 2MASSJ05352184-0546085 taken at the two opposite radial velocity maxima. Comparisons of the TiO bands to model and template spectra are fully consistent with the temperatures previously derived for this system. In particular, the reversal of temperatures with mass - in which the higher-mass primary is cooler than its companion - is confirmed. We measure the projected rotation velocities of the compononents; the primary is rotating at least twice as rapidly as the secondary. At the two radial velocity maxima, Halpha emission lines of both components stick out to either sides of the Halpha central wavelength, which is dominated by nebula emission. This enables us to model the individual Halpha lines of the primary and the secondary. We find that the Halpha emission from the primary is at least 7 times stronger than the emission from the secondary. We conclude that the temperature reversal is very likely due to strong magnetic fields inhibiting convection on the primary.
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New photometric observations of the hierarchical eclipsing TY CrA system were taken in the optical with VYSOS6 and in the near-IR with SOFI and REMIR. They are the first observations showing the deep eclipse minimum of the pre-main sequence secondary in the near-IR. For the first time, the secondary minimum can be reliably used in the calculation of the O-C diagram of TY CrA. By now, the O-C diagram can be studied on a time basis of about two decades. We confirm, that the O-C diagram cannot be explained by the spectroscopic tertiary. For the first time, the light curve of the inner eclipsing binary is analysed in both optical and near-IR bands simultaneously. In combination with already published spectroscopic elements, precise absolute dimensions and masses of the primary and the secondary component are obtained using the ROCHE code. The inclusion of the near-IR data puts strong constraints on the third light which is composed of the reflection nebula, the spectroscopic tertiary and a visual fourth component. The absolute parameters of the inner eclipsing binary agree very well with previous work except of the primary radius (1.46+/-0.15 Rsun) and luminosity (40+/-10 Lsun) which are clearly smaller. While the parameters of the secondary are well understood when assuming an age of about 3-5 Myrs, the primary seems considerably undersized. Low metallicity cannot explain the parameters of the primary.
[not part of Research Note] We report the discovery of a widely-separated low-mass binary as a candidate member of the $sim$40 Myr Argus Association. Resolved imaging and astrometry with 2MASS and LDSS-3 reveal a common proper motion pair of red sources separated by 4.23$pm$0.11, with the secondary roughly one magnitude fainter at $i$, $z$ and $J$. Resolved spectroscopy indicates component types of M8pec and M9pec, the peculiarities arising from weak Na I and strong VO absorption characteristic of low gravity sources. With its small proper motion and estimated 75$pm$25 pc distance, the BANYAN II tool indicates a membership probability of 93% in Argus, which would be consistent with a pair of brown dwarfs of mass $sim$0.04 M$_{odot}$ separated by $sim$300 AU.
We report on observations of the eclipsing binary 2MASS 19090585+4911585 with the 25 cm auxiliary telescope of the University Observatory Jena. We show that a nearby brighter star (2MASS 19090783+4912085) was previously misclassified as the eclipsing binary and find 2MASS 19090585+4911585 to be the true source of variation. We present photometric analysis of VRI light curves. The system is an overcontact binary of W UMa type with an orbital period of (0.288374 +/- 0.000010) d.
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