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Register a new userMeasuring Be depletion in cool stars with exoplanets
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We present new UVES spectra of a sample of 14 mostly cool unevolved stars with planetary companions with the aim of studying possible differences in Be abundance with respect to stars without detected planets. We determine Be abundances for these stars that show an increase in Be depletion as we move to lower temperatures. We carry out a differential analysis of spectra of analog stars with and without planets to establish a possible difference in Be content. While for hot stars no measurable difference is found in Be, for the only cool (Teff ~ 5000 K) planet host star with several analogs in the sample we find enhanced Be depletion by 0.25 dex. This is a first indication that the extra-depletion of Li in solar-type stars with planets may also happen for Be, but shifted towards lower temperatures (Teff < 5500 K) due to the depth of the convective envelopes. The processes that take place in the formation of planetary systems may affect the mixing of material inside their host stars and hence the abundances of light elements.
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We present new UVES spectra of a sample of 15 cool unevolved stars with and without detected planetary companions. Together with previous determinations, we study Be depletion and possible differences in Be abundances between both groups of stars. We obtain a final sample of 89 and 40 stars with and without planets, respectively, which covers a wide range of effective temperatures, from 4700 K to 6400 K, and includes several cool dwarf stars for the first time. We determine Be abundances for these stars and find that for most of them (the coolest ones) the BeII resonance lines are often undetectable, implying significant Be depletion. While for hot stars Be abundances are aproximately constant, with a slight fall as Teff decreases and the Li-Be gap around 6300 K, we find a steep drop of Be content as Teff decreases for Teff < 5500 K, confirming the results of previous papers. Therefore, for these stars there is an unknown mechanism destroying Be that is not reflected in current models of Be depletion. Moreover, this strong Be depletion in cool objects takes place for all the stars regardless of the presence of planets, thus, the effect of extra Li depletion in solar-type stars with planets when compared with stars without detected planets does not seem to be present for Be, although the number of stars at those temperatures is still small to reach a final conclusion.
The large majority of stars in the Milky Way are late-type dwarfs, and the frequency of low-mass exoplanets in orbits around these late-type dwarfs appears to be high. In order to characterize the radiation environments and habitable zones of the cool exoplanet host stars, stellar radius and effective temperature, and thus luminosity, are required. It is in the stellar low-mass regime, however, where the predictive power of stellar models is often limited by sparse data volume with which to calibrate the methods. We show results from our CHARA survey that provides directly determined stellar parameters based on interferometric diameter measurements, trigonometric parallax, and spectral energy distribution fitting.
Stellar flares, winds and coronal mass ejections form the space weather. They are signatures of the magnetic activity of cool stars and, since activity varies with age, mass and rotation, the space weather that extra-solar planets experience can be very different from the one encountered by the solar system planets. How do stellar activity and magnetism influence the space weather of exoplanets orbiting main-sequence stars? How do the environments surrounding exoplanets differ from those around the planets in our own solar system? How can the detailed knowledge acquired by the solar system community be applied in exoplanetary systems? How does space weather affect habitability? These were questions that were addressed in the splinter session Cool stars and Space Weather, that took place on 9 Jun 2014, during the Cool Stars 18 meeting. In this paper, we present a summary of the contributions made to this session.
The relative abundances of carbon and oxygen have long been recognized as fundamental diagnostics of stellar chemical evolution. Now, the growing number of exoplanet observations enable estimation of these elements in exoplanetary atmospheres. In hot Jupiters, the C/O ratio affects the partitioning of carbon in the major observable molecules, making these elements diagnostic of temperature structure and composition. Here we present measurements of carbon and oxygen abundances in 16 stars that host transiting hot Jupiter exoplanets, and compare our C/O ratios to those measured in larger samples of host stars, as well as those estimated for the corresponding exoplanet atmospheres. With standard stellar abundance analysis we derive stellar parameters as well as [C/H] and [O/H] from multiple abundance indicators, including synthesis fitting of the [O I] 6300 {AA} line and NLTE corrections for the O I triplet. Our results, in agreement with recent suggestions, indicate that previously-measured exoplanet host star C/O ratios may have been overestimated. The mean transiting exoplanet host star C/O ratio from this sample is 0.54 (C/O$_{solar}$=0.54), versus previously-measured C/O$_{host~star}$ means of $sim$0.65-0.75. We also observe the increase in C/O with [Fe/H] expected for all stars based on Galactic chemical evolution; a linear fit to our results falls slightly below that of other exoplanet host stars studies but has a similar slope. Though the C/O ratios of even the most-observed exoplanets are still uncertain, the more precise abundance analysis possible right now for their host stars can help constrain these planets formation environments and current compositions.
We present high resolution (R = 100,000) L-band spectroscopy of 11 Herbig AeBe stars with circumstellar disks. The observations were obtained with the VLT/CRIRES to detect hot water and hydroxyl radical emission lines previously detected in disks around T Tauri stars. OH emission lines are detected towards 4 disks. The OH P4.5 (1+,1-) doublet is spectrally resolved as well as the velocity profile of each component of the doublet. Its characteristic double-peak profile demonstrates that the gas is in Keplerian rotation and points to an emitting region extending out to ~ 15-30 AU. The OH, emission correlates with disk geometry as it is mostly detected towards flaring disks. None of the Herbig stars analyzed here show evidence of hot water vapor at a sensitivity similar to that of the OH lines. The non-detection of hot water vapor emission indicates that the atmosphere of disks around Herbig AeBe stars are depleted of water molecules. Assuming LTE and optically thin emission we derive a lower limit to the OH/H2O column density ratio > 1 - 25 in contrast to T Tauri disks for which the column density ratio is 0.3 -- 0.4.
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