15135996
ADONIS observations of hard X-ray emitting late B-type stars in Lindroos systems ?
We present adaptive optics JHK S imaging observations of three main-sequence late B-type stars listed in the Lindroos Catalogue: HD 123445, HD 127971 and HD 129791. Given their spectral types, these stars should not be X-ray emitters. However, they have been detected by ROSAT and their X-ray emission has been attributed to possible unresolved late-type companions. We have carried out near-IR observations with ADONIS at the ESO 3.6 m but have not detected any late-type companions close to HD 127971 and HD 129791. This result leads us to conclude that either (i) they are spectroscopic binaries with unresolved low-mass companions, or (ii) they are intrinsic X-ray emitters. While the former case would be consistent with the reported high multiplicity of early-type (A and B) stars, the latter would yield a revision of stellar activity theories which do not predict X-ray emission from these stars. On the other hand, HD 123445 does indeed show visual companions, namely an apparent subarcsecond faint ($K_{\rm s}\sim10$) binary system at a projected separation of 5´´from the late-B type star. The JHK S magnitudes and colors of the components are consistent with (i) a pair of Pre Main Sequence (PMS) K-type stars at 140 pc (i.e. possible members of the Upper Centaurus Lupus association), (ii) a pair of Main Sequence M-type stars at 60 pc and (iii) a pair of K-type giants at 2.6 kpc. While in the first case the reported X-ray emission can be ascribed to the new objects, in the second and third case it cannot, and we have to assume the late B-type star to be either a spectroscopic binary itself or a single star with intrinsic X-ray emission. Spectroscopy is required to confirm the possible PMS nature of the new binary and Chandra X-ray high spatial resolution (astrometric) imaging observations are required to definitely determine the source of the X-ray emission. If the B9 star results to be the X-ray emitter, near-IR spectroscopy can be used to investigate the presence of a T Tauri like spectroscopic companions.
1110969
OB Associations, Open Clusters, and the Luminosity Calibration of the Nearer Stars
In the context of the luminosity calibration of the nearer stars I discuss the Hipparcos results on distances to nearby OB associations and open clusters. The shortcomings and assumptions in the analyses used to derive these results are pointed out and for the open clusters a comparison is made with results obtained from main sequence fitting. I conclude that given the considerable uncertainties in the latter technique there is no convincing evidence that the Hipparcos based distances to open clusters beyond the Hyades should not be trusted.
11339076
Learning about Galactic structure with Gaia astrometry
The Gaia mission is reviewed together with the expected contents of the final catalogue. It is then argued that the ultimate goal of Galactic structure studies with Gaia astrometry should be to build a dynamical model of our galaxy which is capable of explaining the contents of the Gaia catalogue. This will be possible only by comparing predicted catalogue data to Gaia’s actual measurements. To complement this approach the Gaia catalogue should be used to recalibrate photometric distance and abundance indicators across the HR‐diagram in order to overcome the lack of precise parallax data at the faint end of the astrometric survey. Using complementary photometric and spectroscopic data from other surveys will be essential in this respect.
118384535
Digging supplementary buried channels: investigating the notch architecture within the CCD pixels on ESA's Gaia satellite
The European Space Agency (ESA) Gaia satellite has 106 CCD image sensors which will suffer from increased charge transfer inefficiency (CT I) as a result of radiation damage. To aid the mitigation at low signal levels, the CCD design includes Supplementary Buried Channels (SBCs, otherwise known as ‘notches’) within each C CD column. We present the largest published sample of Gaia CCD SBC Full Well Capacity (FWC) laboratory measurements and simulations based on 13 devices. We find that Gaia CCDs manufactured post-2004 have SBCs with FWCs in the upper half of each CCD that are systematically smaller by two orders of magnitude (650 electrons) compared to those manufactured pre-2004 (thousands of electrons). Gaia’s faint star ( 13 6 G 6 20 mag) astrometric performance predictions by Prod’homme et al. and Holl et al. use pre-2004 SBC FWCs as inputs to their simulations. However, all the CCDs already integrated onto the satellite for the 2013 launch are post2004. SBC FWC measurements are not available for one of our fiv e post-2004 CCDs but the fact it meets Gaia’s image location requirements suggests it has SBC FWCs simi lar to pre2004. It is too late to measure the SBC FWCs onboard the satellite and it is not possible to theoretically predict them. Gaia’s faint star astrometric performance predictions depend o n knowledge of the onboard SBC FWCs but as these are currently unavailable, it is not known how representative of the whole focal plane the current predictions are. Therefore, we suggest Gaia’s initial in-orbit calibrations should include measureme nt of the onboard SBC FWCs. We present a potential method to do this. Faint star astrometric performance predictions based on onboard SBC FWCs at the start of the mission would allow satellite operating conditions or CTI software mitigation to be further optimised to improve the scientific return of Gaia.
53618836
Design drivers for a wide-field multi-object spectrograph for the William Herschel Telescope
Wide-field multi-object spectroscopy is a high priority for European astronomy over the next decade. Most 8-10m telescopes have a small field of view, making 4-m class telescopes a particularly attractive option for wide-field instruments. We present a science case and design drivers for a wide-field multi-object spectrograph (MOS) with integral field units for the 4.2-m William Herschel Telescope (WHT) on La Palma. The instrument intends to take advantage of a future prime-focus corrector and atmospheric-dispersion corrector (Agocs et al, this conf.) that will deliver a field of view 2 deg in diameter, with good throughput from 370 to 1,000 nm. The science programs cluster into three groups needing three different resolving powers R: (1) high-precision radial-velocities for Gaia-related Milky Way dynamics, cosmological redshift surveys, and galaxy evolution studies (R = 5,000), (2) galaxy disk velocity dispersions (R = 10,000) and (3) high-precision stellar element abundances for Milky Way archaeology (R = 20,000). The multiplex requirements of the different science cases range from a few hundred to a few thousand, and a range of fibre-positioner technologies are considered. Several options for the spectrograph are discussed, building in part on published design studies for E-ELT spectrographs. Indeed, a WHT MOS will not only efficiently deliver data for exploitation of important imaging surveys planned for the coming decade, but will also serve as a test-bed to optimize the design of MOS instruments for the future E-ELT.
119117067
ELSA and the frontiers of astrometry
ELSA stands for the ambitious goal of “European Leadership in Space Astrometry”. In this closing contribution I will examine how the ELSA network has advanced this goal. I also look ahead to the time when the Gaia data will be published and consider what needs to be done to maintain European leadership.
119263159
Evaluating the Gamma-Ray Evidence for Self-Annihilating Dark Matter from the Virgo Cluster
Based on three years of Fermi Large Area Telescope (LAT) gamma-ray data of the Virgo cluster, evidence for an extended emission associated with dark matter pair annihilation in the b b-bar channel has been reported by Han et al. [1]. After an in depth spatial and temporal analysis, we argue that the tentative evidence for a gamma-ray excess from the Virgo cluster is mainly due to the appearance of a population of previously unresolved gamma-ray point sources in the region of interest. These point sources are not part of the LAT second source catalogue (2FGL), but are found to be above the standard detection significance threshold when three or more years of LAT data is included.
119188552
Giant Leaps and Minimal Branes in Multi-Dimensional Flux Landscapes
There is a standard story about decay in multi-dimensional flux landscapes: that from any state, the fastest decay is to take a small step, discharging one flux unit at a time; that fluxes with the same coupling constant are interchangeable; and that states with N units of a given flux have the same decay rate as those with -N. We show that this standard story is false. The fastest decay is a giant leap that discharges many different fluxes in unison; this decay is mediated by a 'minimal' brane that wraps the internal manifold and exhibits behavior not visible in the effective theory. We discuss the implications for the cosmological constant.
119096360
Downloading the nuclear structure shell model code OXBASH from INTERNET
This document explains how to download the OXBASH code for nuclear structure calculations from the NSCL anonymous server and get it running on VAX (VMS), ALPHA (OpenVMS) and IBM RS/6000 (aix) computers. The physics behind the code is explained in the OXBASH manual, which is part of the downloading package. Everybody is welcome to download the code and use it under the conditions described below.
117836000
A search for close companions in Sco OB2
Using adaptive optics we study the binary population in the nearby OB association Scorpius OB2. We present the first results of our near-infrared adaptive optics survey among 199 (mainly) A- and B-type stars in Sco OB2. In total 151 components other than the target stars are found, out of which 77 are probably background stars. Our findings are compared with data collected from literature. Out of the remaining 74 candidate physical companions 42 are new, demonstrating that many stars A/B stars have faint, close companions.
16615817
Populating the whole landscape.
Every de Sitter vacuum can transition to every other de Sitter vacuum despite any obstacle, despite intervening anti-de Sitter sinks, despite not being connected by an instanton. Eternal inflation populates the whole landscape.