High Contrast Imaging with Spitzer : Constraining the Frequency of Giant Planets out to 1000 AU separations

We report results of a re-analysis of archival Spitzer IRAC direct imaging surveys encompassing a variety of nearby stars. Our sample is generated from the combined observations of 73 young stars (median age, distance, spectral type = 85 Myr, 23.3 pc, G5) and 48 known exoplanet host stars with unconstrained ages (median distance, spectral type = 22.6 pc, G5). While the small size of Spitzer provides a lower resolution than 8m-class AO-assisted ground based telescopes, which have been used for constraining the frequency of 0.5 - 13 $M_J$ planets at separations of $10 - 10^2$ AU, its exquisite infrared sensitivity provides the ability to place unmatched constraints on the planetary populations at wider separations. Here we apply sophisticated high-contrast techniques to our sample in order to remove the stellar PSF and open up sensitivity to planetary mass companions down to 5\arcsec\ separations. This enables sensitivity to 0.5 - 13 $M_J$ planets at physical separations on the order of $10^2 - 10^3$ AU , allowing us to probe a parameter space which has not previously been systematically explored to any similar degree of sensitivity. Based on a colour and proper motion analysis we do not record any planetary detections. Exploiting this enhanced survey sensitivity, employing Monte Carlo simulations with a Bayesian approach, and assuming a mass distribution of $dn/dm \propto m^{-1.31}$, we constrain (at 95% confidence) a population of 0.5 - 13 $M_J$ planets at separations of 100 - 1000 AU with an upper frequency limit of 9%.Comment: 21 pages, 9 figures, 3 tables, accepted for publication in Ap

Binaries among low-mass stars in nearby young moving groups

The solar galactic neighbourhood contains a number of young co-moving associations of stars (so-called `young moving groups') with ages of ~10--150 Myr, which are prime targets for a range of scientific studies, including direct imaging planet searches. The late-type stellar population of such groups still remain in their pre-main sequence phase, and are thus well suited for purposes such as isochronal dating. Close binaries are particularly useful in this regard, since they allow for a model-independent dynamical mass determination. Here we present a dedicated effort to identify new close binaries in nearby young moving groups, through high-resolution imaging with the AstraLux Sur Lucky Imaging camera. We surveyed 181 targets, resulting in the detection of 61 companions or candidates, of which 38 are new discoveries. An interesting example of such a case is 2MASS J00302572-6236015 AB, which is a high-probability member of the Tucana-Horologium moving group, and has an estimated orbital period of less than 10 years. Among the previously known objects is a serendipitous detection of the deuterium burning boundary circumbinary companion 2MASS J01033563-5515561 (AB)b in the z'-band, thereby extending the spectral coverage for this object down to near-visible wavelengths.Comment: 12 pages, 3 figures, accepted for publication in A&

The discrepancy between dynamical and theoretical mass in the triplet-system 2MASS J10364483+1521394

We combine new Lucky Imaging astrometry from NTT/AstraLux Sur with already published astrometry from the AstraLux Large M-dwarf Multiplicity Survey to compute orbital elements and individual masses of the 2MASS J10364483+1521394 triple system belonging to the Ursa-Major moving group. The system consists of one primary low-mass M-dwarf orbited by two less massive companions, for which we determine a combined dynamical mass of $M_{\rm{B}+\rm{C}}= 0.48 \pm 0.14\ M_\odot$. We show from the companions relative motions that they are of equal mass (with a mass ratio of$1.00 \pm 0.03$), thus$0.24 \pm 0.07\ M_\odot$individually, with a separation of$3.2 \pm 0.3\ $AU and conclude that these masses are significantly higher ($30\%$) than what is predicted by theoretical stellar evolutionary models. The biggest uncertainty remains the distance to the system, here adopted as$20.1 \pm 2.0$pc based on trigonometric parallax, whose ambiguity has a major impact on the result. With the new observational data we are able to conclude that the orbital period of the BC pair is$8.41^{+0.04}_{-0.02}\ $years.Comment: 9 pages, 7 figures, accepted for publication in Astronomy & Astrophysic

Multiple novel prostate cancer susceptibility signals identified by fine-mapping of known risk loci among Europeans

Genome-wide association studies (GWAS) have identified numerous common prostate cancer (PrCa) susceptibility loci. We have fine-mapped 64 GWAS regions known at the conclusion of the iCOGS study using large-scale genotyping and imputation in 25 723 PrCa cases and 26 274 controls of European ancestry. We detected evidence for multiple independent signals at 16 regions, 12 of which contained additional newly identified significant associations. A single signal comprising a spectrum of correlated variation was observed at 39 regions; 35 of which are now described by a novel more significantly associated lead SNP, while the originally reported variant remained as the lead SNP only in 4 regions. We also confirmed two association signals in Europeans that had been previously reported only in East-Asian GWAS. Based on statistical evidence and linkage disequilibrium (LD) structure, we have curated and narrowed down the list of the most likely candidate causal variants for each region. Functional annotation using data from ENCODE filtered for PrCa cell lines and eQTL analysis demonstrated significant enrichment for overlap with bio-features within this set. By incorporating the novel risk variants identified here alongside the refined data for existing association signals, we estimate that these loci now explain ∼38.9% of the familial relative risk of PrCa, an 8.9% improvement over the previously reported GWAS tag SNPs. This suggests that a significant fraction of the heritability of PrCa may have been hidden during the discovery phase of GWAS, in particular due to the presence of multiple independent signals within the same regio

Binaries among low-mass stars in nearby young moving groups

The solar galactic neighborhood contains a number of young co-moving associations of stars (known as young moving groups) with ages of ~10–150 Myr, which are prime targets for a range of scientific studies, including direct imaging planet searches. The late-type stellar populations of such groups still remain in their pre-main sequence phase, and are thus well suited for purposes such as isochronal dating. Close binaries are particularly useful in this regard since they allow for a model-independent dynamical mass determination. Here we present a dedicated effort to identify new close binaries in nearby young moving groups, through high-resolution imaging with the AstraLux Sur Lucky Imaging camera. We surveyed 181 targets, resulting in the detection of 61 companions or candidates, of which 38 are new discoveries. An interesting example of such a case is 2MASS J00302572-6236015 AB, which is a high-probability member of the Tucana-Horologium moving group, and has an estimated orbital period of less than 10 yr. Among the previously known objects is a serendipitous detection of the deuterium burning boundary circumbinary companion 2MASS J01033563-5515561 (AB)b in the z′ band, thereby extending the spectral coverage for this object down to near-visible wavelengths

A Radial velocity survey of spatially resolved young, low-mass binaries

The identification and characterisation of low-mass binaries is of importance for a range of astrophysical investigations. Low-mass binaries in young (∼10–100 Myr) moving groups (YMGs) in the solar neighborhood are of particular significance as they provide unique opportunities to calibrate stellar models and evaluate the ages and coevality of the groups themselves. Low-mass M-dwarfs have pre-main sequence life times on the order of ∼100 Myr and therefore are continually evolving along a mass-luminosity track throughout the YMG phase, providing ideal laboratories for precise isochronal dating, if a model-independent dynamical mass can be measured. AstraLux lucky imaging multiplicity surveys have recently identified hundreds of new YMG low-mass binaries, where a subsample of M-dwarf multiples have estimated orbital periods less than 50 yr. We have conducted a radial velocity survey of a sample of 29 such targets to complement the astrometric data. This will allow enhanced orbital determinations and precise dynamical masses to be derived in a shorter timeframe than possible with astrometric monitoring alone, and allow for a more reliable isochronal analysis. Here we present radial velocity measurements derived for our sample over several epochs. We report the detection of the three-component spectroscopic multiple 2MASS J05301858-5358483, for which the C component is a new discovery, and forms a tight pair with the B component. Originally identified as a YMG member, we find that this system is a likely old field interloper, whose high chromospheric activity level is caused by tidal spin-up of the tight BC pair. Two other triple systems with a tight pair exist in the sample, 2MASS J04244260-0647313 (previously known) and 2MASS J20163382-0711456, but for the rest of the targets we find that additional tidally synchronized companions are highly unlikely, providing further evidence that their high chromospheric activity levels are generally signatures of youth

Multiphoton single and double ionization of neon in the EUV

New information demonstrating the importance of both sequential and simultaneous (or direct) multiphoton ionization of inner shell electrons from neon is discussed in this paper. Ne was irradiated with intense 93 eV free electron laser (FEL) pulses at FLASH and studied with the aid of photoelectron spectrometry. This resulted in two and three photon, single and double ionization of neon, removing electrons from 2s and 2p subshells of the neutral Ne atom in multiple different pathways. The spectral features of the photoelectrons were identified through comparison with the NIST database and field averaged time-dependent density matrix theory. The calculations show the direct multiphoton ionization processes to be extremely sensitive to the focused FEL intensity