The spectral signature of an exoplanet can be separated from the spectrum of its host star using high-resolution spectroscopy. During such observations, the radial component of the planets orbital velocity changes, resulting in a significant Doppler
shift which allows its spectral features to be extracted. Aims: In this work, we aim to detect TiO in the optical transmission spectrum of HD 209458b. Gaseous TiO has been suggested as the cause of the thermal inversion layer invoked to explain the dayside spectrum of this planet. Method: We used archival data from the 8.2m Subaru Telescope taken with the High Dispersion Spectrograph of a transit of HD209458b in 2002. We created model transmission spectra which include absorption by TiO, and cross-correlated them with the residual spectral data after removal of the dominating stellar absorption features. We subsequently co-added the correlation signal in time, taking into account the change in Doppler shift due to the orbit of the planet. Results: We detect no significant cross-correlation signal due to TiO, though artificial injection of our template spectra into the data indicates a sensitivity down to a volume mixing ratio of ~10E-10. However, cross-correlating the template spectra with a HARPS spectrum of Barnards star yields only a weak wavelength-dependent correlation, even though Barnards star is an M4V dwarf which exhibits clear TiO absorption. We infer that the TiO line list poorly match the real positions of TiO lines at spectral resolutions of ~100,000. Similar line lists are also used in the PHOENIX and Kurucz stellar atmosphere suites and we show that their synthetic M-dwarf spectra also correlate poorly with the HARPS spectra of Barnards star and five other M-dwarfs. We conclude that the lack of an accurate TiO line list is currently critically hampering this high-resolution retrieval technique.
The Kepler object KIC 12557548 shows irregular eclipsing behaviour with a constant 15.685 hr period, but strongly varying transit depth. In this paper we fit individual eclipses, in addition to fitting binned light curves, to learn more about the pro
cess underlying the eclipse depth variation. Additionally, we put forward observational constraints that any model of this planet-star system will have to match. We find two quiescent spells of ~30 orbital periods each where the transit depth is <0.1%, followed by relatively deep transits. Additionally, we find periods of on-off behaviour where >0.5% deep transits are followed by apparently no transit at all. Apart from these isolated events we find neither significant correlation between consecutive transit depths nor a correlation between transit depth and stellar intensity. We find a three-sigma upper limit for the secondary eclipse of 4.9*10^-5, consistent with a planet candidate with a radius of less than 4600 km. Using the short cadence data we find that a 1-D exponential dust tail model is insufficient to explain the data. We improved our model to a 2-D, two-component dust model with an opaque core and an exponential tail. Using this model we fit individual eclipses observed in short cadence mode. We find an improved fit of the data, quantifying earlier suggestions by Budaj (2013) of the necessity of at least two components. We find that deep transits have most absorption in the tail, and not in a disk-shaped, opaque coma, but the transit depth and the total absorption show no correlation with the tail length.
In this paper we present the discovery of a highly unequal-mass eclipsing M-dwarf binary, providing a unique constraint on binary star formation theory and on evolutionary models for low-mass binary stars. The binary is discovered using high- precisi
on infrared light curves from the WFCAM Transit Survey (WTS) and has an orbital period of 2.44 d. We find stellar masses of M1 = 0.53 (0.02) Msun and M2 = 0.143 (0.006) Msun (mass ratio 0.27), and radii of R1 = 0.51 (0.01) Rsun and R2 = 0.174 (0.006) Rsun. This puts the companion in a very sparsely sampled and important late M-dwarf mass-regime. Since both stars share the same age and metallicity and straddle the theoretical boundary between fully and partially convective stellar interiors, a comparison can be made to model predictions over a large range of M-dwarf masses using the same model isochrone. Both stars appear to have a slightly inflated radius compared to 1 Gyr model predictions for their masses, but future work is needed to properly account for the effects of star spots on the light curve solution. A significant, subsynchronous, ~2.56 d signal with ~2% peak-to-peak amplitude is detected in the WFCAM light curve, which we attribute to rotational modulation of cool star spots. We propose that the subsynchronous rotation is either due to a stable star-spot complex at high latitude on the (magnetically active) primary (i.e. differential rotation), or to additional magnetic braking, or to interaction of the binary with a third body or circumbinary disk during its pre-main-sequence phase.
The giant planet orbiting tau Bootis was among the first extrasolar planets to be discovered through the reflex motion of its host star. It is one of the brightest known and most nearby planets with an orbital period of just a few days. Over the cour
se of more than a decade, measurements of its orbital inclination have been announced and refuted, and have subsequently remained elusive until now. Here we report on the detection of carbon monoxide absorption in the thermal day-side spectrum of tau Bootis b. At a spectral resolution of R~100,000, we trace the change in the radial velocity of the planet over a large range in phase, determining an orbital inclination of i=44.5+-1.5 degrees and a true planet mass of 5.95+-0.28 MJup. This result extends atmospheric characterisation to non-transiting planets. The strong absorption signal points to an atmosphere with a temperature that is decreasing towards higher altitudes. This is a stark contrast to the temperature inversion invoked for other highly irradiated planets, and supports models in which the absorbing compounds believed to cause such atmospheric
One of the biggest challenges facing large transit surveys is the elimination of false-positives from the vast number of transit candidates. We investigate to what extent information from the lightcurves can identify blend scenarios and eliminate the
m as planet candidates, to significantly decrease the amount of follow-up observing time required to identify the true exoplanet systems. If a lightcurve has a sufficiently high signal-to-noise ratio, a distinction can be made between the lightcurve of a stellar binary blended with a third star and the lightcurve of a transiting exoplanet system. We perform simulations to determine what signal-to-noise level is required to make the distinction between blended and non-blended systems as function of transit depth and impact parameter. Subsequently we test our method on real data from the first IRa01 field observed by the CoRoT satellite, concentrating on the 51 candidates already identified by the CoRoT team. About 70% of the planet candidates in the CoRoT IRa01 field are best fit with an impact parameter of b>0.85, while less than 15% are expected in this range considering random orbital inclinations. By applying a cut at b<0.85, meaning that ~15% of the potential planet population would be missed, the candidate sample decreases from 41 to 11. The lightcurves of 6 of those are best fit with such low host star densities that the planet-to-star size ratii imply unrealistic planet radii of R>2RJup. Two of the five remaining systems, CoRoT1b and CoRoT4b, have been identified as planets by the CoRoT team, for which the lightcurves alone rule out blended light at 14% (2sigma) and 31% (2sigma). We propose to use this method on the Kepler database to study the fraction of real planets and to potentially increase the efficiency of follow-up.
We report on the discovery of four ultra-short period (P<0.18 days) eclipsing M-dwarf binaries in the WFCAM Transit Survey. Their orbital periods are significantly shorter than of any other known main-sequence binary system, and are all significantly
below the sharp period cut-off at P~0.22 days as seen in binaries of earlier type stars. The shortest-period binary consists of two M4 type stars in a P=0.112 day orbit. The binaries are discovered as part of an extensive search for short-period eclipsing systems in over 260,000 stellar lightcurves, including over 10,000 M-dwarfs down to J=18 mag, yielding 25 binaries with P<0.23 days. In a popular paradigm, the evolution of short period binaries of cool main-sequence stars is driven by loss of angular momentum through magnetised winds. In this scheme, the observed P~0.22 day period cut-off is explained as being due to timescales that are too long for lower-mass binaries to decay into tighter orbits. Our discovery of low-mass binaries with significantly shorter orbits implies that either these timescales have been overestimated for M-dwarfs, e.g. due to a higher effective magnetic activity, or that the mechanism for forming these tight M-dwarf binaries is different from that of earlier type main-sequence stars.
Young radio-loud active galactic nuclei form an important tool to investigate the evolution of extragalactic radio sources. To study the early phases of expanding radio sources, we have constructed CORALZ, a sample of 25 compact ($theta<2$) radio sou
rces associated with nearby ($z<0.16$) galaxies. In this paper we determine the morphologies, linear sizes, and put first constraints on the lobe expansion speeds of the sources in the sample. We observed the radio sources from the CORALZ sample with MERLIN at 1.4 GHz or 1.6 GHz, the EVN at 1.6 GHz, and global VLBI at 1.6 GHz and/or 5.0 GHz. Radio maps, morphological classifications, and linear sizes are presented for all sources in the CORALZ sample. We have determined a first upper limit to the expansion velocity of one of the sources, which is remarkably low compared to the brighter GPS sources at higher redshifts, indicating a relation between radio luminosity and expansion speed, in agreement with analytical models. In addition we present further strong evidence that the spectral turnovers in GPS and CSS sources are caused by synchrotron self-absorption (SSA): the CORALZ sources are significantly offset from the well-known correlation between spectral peak frequency and angular size, but this correlation is recovered after correcting for the flux-density dependence, as predicted by SSA theory.
Context: Photometric observations for the OGLE-II microlens monitoring campaign have been taken in the period 1997-2000. All light curves of this campaign have recently been made public. Our analysis of these data has revealed 13 low-amplitude transi
ting objects among ~15700 stars in three Carina fields towards the galactic disk. One of these objects, OGLE2-TR-L9 (P~2.5 days), turned out to be an excellent transiting planet candidate. Aims: In this paper we report on our investigation of the true nature of OGLE2-TR-L9, by re-observing the photometric transit with the aim to determine the transit parameters at high precision, and by spectroscopic observations, to estimate the properties of the host star, and to determine the mass of the transiting object through radial velocity measurements. Methods: High precision photometric observations have been obtained in g, r, i, and z band simultaneously, using the new GROND detector, mounted on the MPI/ESO 2.2m telescope at La Silla. Eight epochs of high-dispersion spectroscopic observations were obtained using the fiber-fed FLAMES/UVES Echelle spectrograph, mounted on ESOs Very Large Telescope at Paranal. Results: The photometric transit, now more than 7 years after the last OGLE-II observations, was re-discovered only ~8 minutes from its predicted time. The primary object is a fast rotating F3 star, with vsini=39.33+-0.38 km/s, T=6933+-58 K, log g = 4.25+-0.01, and [Fe/H] = -0.05+-0.20. The transiting object is an extrasolar planet with M_p=4.5+-1.5 M_Jup and R_p=1.61+-0.04 R_Jup. The rejection of possible blend scenarios was based on a quantitative analysis of the multi-color photometric data [abridged].
[Context] The first detection of an atmosphere around an extrasolar planet was presented by Charbonneau and collaborators in 2002. In the optical transmission spectrum of the transiting exoplanet HD209458b, an absorption signal from sodium was measur
ed at a level of 0.023+-0.006%, using the STIS spectrograph on the Hubble Space Telescope. Despite several attempts, so far only upper limits to the Na D absorption have been obtained using telescopes from the ground, and the HST result has yet to be confirmed. [Aims] The aims of this paper are to re-analyse data taken with the High Dispersion Spectrograph on the Subaru telescope, to correct for systematic effects dominating the data quality, and to improve on previous results presented in the literature. [Methods] The data reduction process was altered in several places, most importantly allowing for small shifts in the wavelength solution. The relative depth of all lines in the spectra, including the two sodium D lines, are found to correlate strongly with the continuum count level in the spectra. These variations are attributed to non-linearity effects in the CCDs. After removal of this empirical relation the uncertainties in the line depths are only a fraction above that expected from photon statistics. [Results] The sodium absorption due to the planets atmosphere is detected at >5 sigma, at a level of 0.056+-0.007% (2x3.0 Ang band), 0.070+-0.011% (2x1.5 Ang band), and 0.135+-0.017% (2x0.75 Ang band). There is no evidence that the planetary absorption signal is shifted with respect to the stellar absorption, as recently claimed for HD189733b. The measurements in the two most narrow bands indicate that some signal is being resolved.[abridged]
A short overview is given of the status of research on young extragalactic radio sources. We concentrate on Very Long Baseline Interferometric (VLBI), and space-VLBI results obtained with the VLBI Space Observatory Programme (VSOP). In 2012, VSOP-2 w
ill be launched, which will allow VLBI observations at an unprecedented angular resolution. One particular question VSOP-2 could answer is whether some of the High Frequency Peakers (HFP) are indeed the youngest objects in the family of GPS and CSS sources. VSOP-2 observations can reveal their angular morphology and determine whether any are Ultra-compact Symmetric Objects.
