Search

We obtained 238 spectra of the close orbiting extrasolar giant planet HD 189733b with resolution R ~ 15,000 during one night of observations with the near infrared spectrograph, NIRSPEC, at the Keck II Telescope. We have searched for planetary absorption signatures in the 2.0 - 2.4 micron region where H_2O and CO are expected to be the dominant atmospheric opacities. We employ a phase dependent orbital model and tomographic techniques to search for the planetary absorption signatures in the combined stellar and planetary spectra. Because potential absorption signatures are hidden in the noise of each single exposure, we use a model list of lines to apply a spectral deconvolution. The resulting mean profile possesses a S/N ratio that is 20 times greater than that found in individual lines. Our spectral timeseries thus yields spectral signatures with a mean S/N = 2720. We are unable to detect a planetary signature at a contrast ratio of log_10(F_p/F_*) = -3.40, with 63.8 per cent confidence. Our findings are not consistent with model predictions which nevertheless give a good fit to mid-infrared observations of HD 189733. The 1-sigma result is a factor of 1.7 times less than the predicted 2.185 micron planet/star flux ratio of log_10(F_p/F_*) ~ -3.16., Comment: 9 pages, 3 Figures

We have performed photometric observations of nearly 7 million stars with 8 < V < 15 with the SuperWASP-North instrument from La Palma between 2004 May-September. Fields in the RA range 17-18hr, yielding over 185,000 stars with sufficient quality data, have been searched for transits using a modified box least-squares (BLS) algorithm. We find a total of 58 initial transiting candidates which have high S/N in the BLS, show multiple transit-like dips and have passed visual inspection. Analysis of the blending and inferred planetary radii for these candidates leaves a total of 7 transiting planet candidates which pass all the tests plus 4 which pass the majority. We discuss the derived parameters for these candidates and their properties and comment on the implications for future transit searches., Comment: 17 pages, 24 figures, accepted by MNRAS

The SuperWASP-I instrument observed 6.7 million stars between 8-15 mag from La Palma during the 2004 May-September season. Our transit-hunting algorithm selected 11,626 objects from the 184,442 stars within the range RA 18hr-21hr. We describe our thorough selection procedure whereby catalogue information is exploited along with careful study of the SuperWASP data to filter out, as far as possible, transit mimics. We have identified 35 candidates which we recommend for follow-up observations., Comment: 20 pages, 7 figures, accepted for publication in MNRAS

We present a search for the near infrared spectroscopic signature of the close orbiting extrasolar giant planet HD 75289b. We obtained ~230 spectra in the wavelength range 2.18 - 2.19 microns using the Phoenix spectrograph at Gemini South. By considering the direct spectrum, derived from irradiated model atmospheres, we search for the absorption profile signature present in the combined star and planet light. Since the planetary spectrum is separated from the stellar spectrum at most phases, we apply a phase dependent orbital model and tomographic techniques to search for absorption signatures. Because the absorption signature lies buried in the noise of a single exposure we apply a multiline deconvolution to the spectral lines available in order to boost the effective S/N ratio of the data. The wavelength coverage of 80 angstroms is expected to contain ~100 planetary lines, enabling a mean line with S/N ratio of ~800 to be achieved after deconvolution. We are nevertheless unable to detect the presence of the planet in the data and carry out further simulations to show that broader wavelength coverage should enable a planet like HD 75289b to be detected with 99.9 per cent (4 sigma) confidence. We investigate the sensitivity of our method and estimate detection tolerances for mismatches between observed and model planetary atmospheres.

The Spitzer-COSMOS survey (S-COSMOS) is a Legacy program (Cycles 2+3) designed to carry out a uniform deep survey of the full 2 sq deg COSMOS field in all seven Spitzer bands (3.6, 4.5, 5.6, 8.0, 24.0, 70.0, 160.0 u). This paper describes the survey parameters, mapping strategy, data reduction procedures, achieved sensitivities to date, and the complete data set for future reference. We show that the observed infrared backgrounds in the S-COSMOS field are within 10% of the predicted background levels. The fluctuations in the background at 24u have been measured and do not show any significant contribution from cirrus, as expected. In addition, we report on the number of asteroid detections in the low galactic latitude COSMOS field. We use the Cycle 2 S-COSMOS data to determine preliminary number counts, and compare our results with those from previous Spitzer Legacy surveys (e.g. SWIRE, GOODS). The results from this "first analysis" confirm that the S-COSMOS survey will have sufficient sensitivity with IRAC to detect ~ L* disks and spheroids out to z ~ 3, and with MIPS to detect ultraluminous starbursts and AGN out to z ~3 at 24u and out to z ~1.5-2 at 70u and 160u., Comment: 21 pages including 4 tables and 9 figures. Accepted for Publication on ApJS COSMOS special Issue

Observations of stellar prominences on young rapidly rotating stars provide unique probes of their magnetic fields out to many stellar radii. We compare two independently obtained datasets of the K3 dwarf Speedy Mic using the Anglo-Australian Telescope (AAT) and the ESO Very Large Telescope (VLT). Taken more than a fortnight apart they provide the first insight into the evolution of the prominence system on such a young rapidly rotating star. The largest prominences observed transiting the stellar disc are found at very similar rotational phases between the epochs. This suggests that the magnetic structures supporting the prominences retain their identity on a two to three week timescale. We identify prominences as transient absorption features in all lines of the Hydrogen Balmer series down to H_10. We use the ratios of the prominence EWs in these lines to determine their column densities in the first excited state of hydrogen. We determine the optical depths, finding prominences to be rather optically thick (\tau \approx 20) in the H_alpha line. The total hydrogen column density and thus the prominence masses are determined via observations of the CaII H&K lines. We find typical masses for four of the largest prominences to be in the range 0.5 - 2.3 x10^{14} kg, slightly larger than giant solar prominence masses. Rotationally modulated emission is seen outside of the H_alpha line. These loops of emission are shown to be caused by prominences seen off the stellar disc. We find that all of the large emission loops can be associated with prominences we see transiting the stellar disc. This combined with the fact that many prominences appear to eclipse the off-disc emission of others, strongly suggests that the prominence system is highly flattened and likely confined to low stellar latitudes., Comment: 13 pages, 7 figures, accepted for publication in MNRAS, (Higher resolution greyscale images can be found at http://star-www.st-and.ac.uk/~njd2/speedy/index.html)

We have used maximum entropy eclipse mapping to recover images of the visual surface brightness distribution of the primary component of the RS CVn eclipsing binary SV Cam, using high-precision photometry data obtained during three primary eclipses with STIS aboard the Hubble Space Telescope. These were augmented by contemporaneous ground-based photometry secured around the rest of the orbit. The goal of these observations was to determine the filling factor and size distribution of starspots too small to be resolved by Doppler imaging. The information content of the final image and the fit to the data were optimised with respect to various system parameters using the chi^2 landscape method, using an eclipse mapping code that solves for large-scale spot coverage. It is only with the unprecedented photometric precision of the HST data (0.00015 mag) that it is possible to see strong discontinuities at the four contact points in the residuals of the fit to the lightcurve. These features can only be removed from the residual lightcurve by the reduction of the photospheric temperature, to synthesise high unresolvable spot coverage, and the inclusion of a polar spot. We show that this spottedness of the stellar surface can have a significant impact on the determination of the stellar binary parameters and the fit to the lightcurve by reducing the secondary radius from 0.794 +/- 0.009 Rsun to 0.727 +/- 0.009 Rsun. This new technique can also be applied to other binary systems with high precision spectrophotometric observations., Comment: 9 pages, 10 figures

We present new observations of the prominence system on the K3 dwarf Speedy Mic (BO Mic, HD 197890). Using an improved technique to track the absorption features in H_alpha we find a very active prominence system with approximately ten prominences on the observable hemisphere per rotation. From a total of 25 prominences we find an average axial distance of 2.85+/-0.54 R_* which is twice the co-rotation radius above the stellar surface. We discuss the consequences of these observations on the nature of the supporting magnetic structures. Two consecutive nights, with complete phase coverage, combined with a further night after a three night gap allow us to study the evolution of the prominence system on two different timescales. Several of the prominences have counterparts at similar phases on consecutive nights. During this interval many prominences show evidence for evolution in their heights and phases of observation. Five nights (13 rotation cycles) later we recover many prominences at approximately the same phases. Whilst individual prominences change axial distances or appear/re-appear from night-to-night the underlying prominence supporting structures appear to be stable over as many as 13 stellar rotations., Comment: 10 pages, 6 figures, accepted for publication in MNRAS, (Higher resolution greyscale images can be found at http://star-www.st-and.ac.uk/~njd2/speedy/index.html)

We present high resolution images of the young rapidly rotating K3 dwarf Speedy Mic (BO Mic, HD 197890). The photospheric spot maps reveal a heavily and uniformly spotted surface from equatorial to high latitude regions. Contrary to many images of similar objects, Speedy Mic does not possess a uniform filling at high latitudes, but exhibits structure in the polar regions showing greatest concentration in a particular longitude range. The asymmetric rotation profile of Speedy Mic indicates the presence of a companion or nearby star which shows radial velocity shifts over a timescale of several years. Using a simple dynamical argument, we show that Speedy Mic is unlikely to be a binary system, and conclude that the feature must be the result of a chance alignment with a background binary. Complete phase coverage on two consecutive nights in addition to 60 per cent phase coverage after a three night gap has enabled us to track the evolution of spots with time. By incorporating a solar-like differential rotation model into the image reconstruction process, we find that the equator laps the polar regions once every $191 \pm 17$ d. This finding is in close agreement with measurements for other late-type rapid rotators.

We have used spectrophotometric data from the Hubble Space Telescope to eclipse-map the primary component of the RS CVn binary SV Cam over 9 HST orbits. We find from these observations and the HIPPARCOS parallax that the surface flux in the eclipsed low-latitude region of the primary is about 30% lower than computed from a PHOENIX model atmosphere at the effective temperature that best fits the spectral energy distribution of the eclipsed flux. This can only be accounted for if about a third of the primary's surface is covered with unresolved dark star-spots. Extending this to the full surface of the primary, we find that even taking into account this spot filling factor there is an additional flux deficit on the primary star. This can only be explained if there is a large polar spot on the primary star extending from the pole to latitude 48 degrees., Comment: 20 pages, 14 figures, accepted by ApJ

Electrical spin injection from the Heusler alloy Co_2MnGe into a p-i-n Al_0.1Ga_0.9As/GaAs light emitting diode is demonstrated. A maximum steady-state spin polarization of approximately 13% at 2 K is measured in two types of heterostructures. The injected spin polarization at 2 K is calculated to be 27% based on a calibration of the spin detector using Hanle effect measurements. Although the dependence on electrical bias conditions is qualitatively similar to Fe-based spin injection devices of the same design, the spin polarization injected from Co_2MnGe decays more rapidly with increasing temperature., Comment: 8 pages, 4 figures

We present Doppler images of the young K5V - K7V rapid rotator LO Peg from seven nights of continuous spectroscopy obtained in 1998 from July 04 to July 10. The images reveal the presence of a strong polar cap with appendages extending to mid-latitudes, but no starspots are seen below 15\degr. We briefly discuss the distribution of spots in light of recent flux transport simulations which are able to reproduce the observed latitude dependence. With the full timeseries of spectra, of which 314 are useful, many phases are observed three times over the seven nights of observations. Using starspots as tracers of a solar-like latitudinal differential rotation in our image reconstructions, we find that the equatorial regions complete one more rotation than the polar regions every {181 $\pm$ 35} d. LO Peg is the second coolest star for which such a measurement has been made using indirect imaging methods. The degree of latitudinal shear is less than that seen in G and early K dwarfs, suggesting a trend in which differential rotation decreases with stellar mass in (pre-)main sequence objects., Comment: 9 pages (to appear in MNRAS)

We use Doppler imaging techniques to determine the dependence of starspot rotation rates on latitude in an homogeneous sample of young, rapidly-rotating solar analogues. A solar-like differential rotation law is used, where the rotation depends on sin$^2$($\theta$), where $\theta$ is the stellar latitude. By including this term in the image reconstruction process, using starspots as tracers, we are able to determine the magnitude of the shear over more than one rotation cycle. We also consider results from matched filter starspot tracking techniques, where individual starspot rotation rates are determined. In addition we have re-analysed published results and present a new measurement for the K3 dwarf, Speedy Mic. A total of 10 stars of spectral type G2 - M2 are considered. We find a trend towards decreasing surface differential rotation with decreasing effective temperature. The implied approach to solid body rotation with increasing relative convection zone depth implies that the dynamo mechanism operating in low-mass stars may be substantially different from that in the Sun., Comment: 5 pages, 3 figures, to appear in MNRAS

We present Doppler Images of the RS CVn binary system HR 1099 (V711 Tau) from spectra taken in two different sites, KPNO and MSO, during the MUSICO S 1998 campaign. Contemporaneous APT photometry is used to constrain the Doppler Images. The resulting maximum entropy reconstructions based on the least-square s deconvolved profiles, derived from $\sim$2000 photospheric absorption lines, r eveal the presence of starspots at medium-high latitudes. We have obtained maps for both components of the binary system for the first time. The predominant str ucture in the primary component is an off-centered polar spot, confirming previo us works on the same target by using independent codes. The result is verified b y using both data sets independently. The lower spectral resolution data set giv es a less detailed map for the MSO data set. The images obtained for the seconda ry component show a low latitude spot around orbital phase 0.7. This spot seems to mirror the structure seen on the primary. It might suggest that tidal forces may influence the spot distribution on this binary system., Comment: 12 pages, 9 figures. Accepted by A&A

We have obtained echelle spectroscopy of 14 Population II objects selected from those previously observed by Bonifacio & Molaro (1997). For one object, HD 140283, we obtained exquisite data with the High Dispersion Spectrograph on the Subaru Telescope, with S/N exceeding 1000 per 0.018A pixel. Li abundances have been determined by spectral synthesis from both the 6708A resonance line and also from 6104A subordinate feature. Firm detections of the weak line have been made in seven objects, and upper limits are reported for the remainder. Our 6708A abundances agree with those reported by Bonifacio & Molaro at the 99%-confidence level. Abundances from the 6104A line hint at a higher Li abundance than that determined from the resonance feature, but this evidence is mixed; the weakness of the 6104A line and the large number of upper limits make it difficult to draw firm conclusions. NLTE-corrections increase (rather than eliminate) the size of the (potential) discrepancy, and binarity appears unlikely to affect any abundance difference. The effect of multi-dimensional atmospheres on the line abundances was also considered, although it appears that use of 3-D (LTE) models could again act to increase the discrepancy, if one is indeed present., Comment: 13 pages, 8 figures

We present new VLA C+D-array HI observations and optical and NIR imaging of the well known interacting system NGC 4038/9, ``The Antennae''. The radio data reveal a wealth of gaseous sub-structure both within the main bodies of the galaxies and along the tidal tails. In agreement with previous HI studies, we find that the northern tail has HI along its outer length, but none along its base. We suggest that the HI at the base of this tail has been ionized by massive stars in the disk of NGC 4038. The gas in the southern tail has a bifurcated structure, with one filament lying along the optical tail and another running parallel to it but with no optical counterpart. The two filaments join just before the location of several star forming regions near the end of the tail. The HI velocity field at the end of the tail is dominated by strong velocity gradients which suggest that at this location the tail is bending away from us. We delineate and examine two regions within the tail previously identified as possible sites of a so-called ``tidal dwarf galaxy'' condensing out of the expanding tidal material. The tail velocity gradients mask any clear kinematic signature of a self-gravitating condensation in this region. A dynamical analysis suggest that there is not enough mass in gas alone for either of these regions to be self-gravitating. Conversely, if they are bound they require a significant contribution to their dynamical mass from evolved stars or dark matter. (Abridged), Comment: 26 pages, 12 figures, requires emulateapj.sty. To Appear in the December 2001 AJ (Vol 122, No. 6). Version with full-resolution figures available at http://www.cv.nrao.edu/~jhibbard/n4038/n4038HI/

WFPC2 images and STIS spectroscopic observations are presented of the double nucleus in the merger system NGC 6240. We find that: (a) the kinematics of the ionized gas is similar to that of the molecular gas, despite a different morphology; (b) the gaseous and stellar kinematics are quite different, suggesting an early merger stage; (c) neither the gaseous nor the stellar kinematics show an obvious sign of the supermassive black hole believed to be responsible for the X-ray emission of NGC 6240; and (d) the steep off-nuclear velocity gradient is not due to a 10E11 solar mass black hole, in contrast to earlier suggestions., Comment: To appear in: "The central kpc of starbursts and AGN: the La Palma connection", Eds. J.H. Knapen, J.E. Beckman, I. Shlosman and T.J. Mahoney, ASP conf. series, in press (2001)

Lithium abundances, radial velocities and rotational velocities are reported for 20 candidate F, G and K stars of the sparse Coma Berenices open cluster. All the stars are proper-motion selected, and our radial velocities support the membership credentials of at least 12 of the candidates. Combining our data with that in the literature, we have a close-to-complete census of Li abundances for late-type stars with Mv < 5.8. These data show that the Li-depletion pattern in Coma Ber is similar, but not identical, to that in the Hyades cluster, which has a similar age but higher metallicity. Several Coma Ber F stars have suffered significantly more Li depletion than their counterparts in the Hyades. The G and early-K stars of Coma Ber have undergone less Li depletion than those of the Hyades, but much more than that predicted by standard evolutionary models featuring only convective mixing. This provides strong evidence for additional mixing and Li depletion operating in these stars during their first 400Myr on the main sequence, amounting to 0.3 dex at 6000K and rising to 0.8-1.2 dex at 5400K. We find that 4 of the radial-velocity non-members are among a small number of low-mass stars which were previously reported as part of an extra-tidal moving group associated with the Coma Ber cluster. As a result we now find that the luminosity function of this moving group is indistinguishable from that of the central cluster. It is uncertain whether there may be a significant number of stars with even lower masses among the moving group., Comment: 12 pages, 4 figures