Astrometric Effects of a Stochastic Gravitational Wave Background

A stochastic gravitational wave background causes the apparent positions of distant sources to fluctuate, with angular deflections of order the characteristic strain amplitude of the gravitational waves. These fluctuations may be detectable with high precision astrometry, as first suggested by Braginsky et al. in 1990. Several researchers have made order of magnitude estimates of the upper limits obtainable on the gravitational wave spectrum \Omega_gw(f), at frequencies of order f ~ 1 yr^-1, both for the future space-based optical interferometry missions GAIA and SIM, and for VLBI interferometry in radio wavelengths with the SKA. For GAIA, tracking N ~ 10^6 quasars over a time of T ~ 1 yr with an angular accuracy of \Delta \theta ~ 10 \mu as would yield a sensitivity level of \Omega_gw ~ (\Delta \theta)^2/(N T^2 H_0^2) ~ 10^-6, which would be comparable with pulsar timing. In this paper we take a first step toward firming up these estimates by computing in detail the statistical properties of the angular deflections caused by a stochastic background. We compute analytically the two point correlation function of the deflections on the sphere, and the spectrum as a function of frequency and angular scale. The fluctuations are concentrated at low frequencies (for a scale invariant stochastic background), and at large angular scales, starting with the quadrupole. The magnetic-type and electric-type pieces of the fluctuations have equal amounts of power.Comment: 23 pages, 2 figures, references added and minor text correction

Kinematics of Black Hole X-ray Binary GRS 1915+105

The space velocity of a stellar black hole encodes the history of its formation and evolution. Here we measure the 3-dimensional motion of the microquasar GRS 1915+105, using a decade of astrometry with the NRAO Very Long Baseline Array, together with the published radial velocity. The velocity in the Galactic Plane deviates from circular rotation by 53-80 +_ 8 km/s, where the range covers any specific distance from 6-12 kpc. Perpendicular to the plane, the velocity is only 10 +_ 4 km/s. The peculiar velocity is minimized at a distance 9-10 kpc, and is then nearly in the radial direction towards the Galactic Center. We discuss mechanisms for the origin of the peculiar velocity, and conclude that it is most likely a consequence of Galactic velocity diffusion on this old binary, rather than the result of a supernova kick during the formation of the 14 Mo black hole. Finally, a brief comparison is made with 4 other BH binaries whose kinematics are well determined.Comment: 16 pages, 4 figures. ApJ accepte

The first accurate parallax distance to a black hole

Using astrometric VLBI observations, we have determined the parallax of the black hole X-ray binary V404 Cyg to be 0.418 +/- 0.024 milliarcseconds, corresponding to a distance of 2.39 +/- 0.14 kpc, significantly lower than the previously accepted value. This model-independent estimate is the most accurate distance to a Galactic stellar-mass black hole measured to date. With this new distance, we confirm that the source was not super-Eddington during its 1989 outburst. The fitted distance and proper motion imply that the black hole in this system likely formed in a supernova, with the peculiar velocity being consistent with a recoil (Blaauw) kick. The size of the quiescent jets inferred to exist in this system is less than 1.4 AU at 22 GHz. Astrometric observations of a larger sample of such systems would provide useful insights into the formation and properties of accreting stellar-mass black holes.Comment: Accepted for publication in ApJ Letters. 6 pages, 2 figure

Prognostic factors for tumour response, progression-free survival and toxicity in metastatic colorectal cancer patients given irinotecan (CPT-11) as second-line chemotherapy after 5FU failure

Our purpose was to determine, in patients with metastatic colorectal carcinoma treated with irinotecan single-agent after 5-FU failure, the most significant predictive parameters for tumour response, progression-free survival and toxicity. Between October 1992 and April 1995, 455 patients with 5-FU resistant metastatic colorectal carcinoma entered four consecutive phase II trials. The first two studies assessed tumour response, the other two were randomized studies which assessed the efficacy of racecadotril to prevent irinotecan-induced diarrhoea. Due to homogeneous main eligibility criterias, data from those studies could be pooled for statistical analysis. Potential clinical and biological predictive factors (PF) for toxicity, tumour growth control, e.g. response or stabilization and progression-free survival (PFS), were studied in multivariate analysis. 363 patients were evaluable for response, 432 were evaluable for PFS, 368 for neutropenia and 416 for delayed diarrhoea, respectively. Normal baseline haemoglobin level (Hb), time since diagnosis of colorectal carcinoma, grade 3 or 4 neutropenia or diarrhoea at first cycle and a low number of organs involved were the most PF for tumour growth control (P< 0.05). Significant prognostic variables for PFS were WHO Performance Status, liver and lymph-node involvement, time since diagnosis, age and CEA value (P≤ 0.02). Six groups of patients based on the number of unfavourable prognostic factors are presented. Baseline bilirubin, haemoglobin level, number of organs involved and time from diagnosis were PF for neutropenia; PS, serum creatinine, leukocyte count, time from 5-FU progression and prior abdominopelvic irradiation were PF for delayed diarrhoea (P≤ 0.05). These PF should help clinicians to anticipate for a given patient the probability to observe a response/stabilization or a toxicity. These results should also be prospectively confirmed in ongoing or future trials using irinotecan, both as a single agent and in combination with other drugs. © 2000 Cancer Research Campaig

Supernovae with "Super-Hipparcos"

GAIA is the ``super-Hipparcos'' satellite scheduled for launch in 2010 by the European Space Agency. It is a scanning satellite that carries out multi-colour, multi-epoch photometry on all objects brighter than 20th magnitude. We conduct detailed simulations of supernovae (SNe) detection by GAIA. Supernovae of each type are chosen according to the observed distributions of absolute magnitudes, and located in nearby galaxies according to the local large-scale structure. Using an extinction model of the Galaxy and the scanning law of the GAIA satellite, we calculate how many SNe are detectable as a function of the phase of the lightcurve. Our study shows that GAIA will report data on 21400 SNe during the five-year mission lifetime, of which 14300 are SNe Ia, 1400 are SNe Ib/c and 5700 are SNe II. Using the simulations, we estimate that the numbers caught before maximum are 6300 SNe Ia, 500 SNe Ib/c and 1700 SNe II. GAIA will issue about 5 SNe alerts a day. The most distant SNe accessible to GAIA are at a redshift of 0.14 and so GAIA will provide a huge sample of local SNe. There will be many examples of the rarer subluminous events, over-luminous events, SNe Ib/c and SNe II-L. SNe rates will be found as a function of galaxy type, as well as extinction and position in the host galaxy. Amongst other applications, there may be about 26 SNe each year for which detection of gravitational waves is possible and about 180 SNe each year for which detection of gamma-rays is possible.Comment: 8 pages, 4 figures, version in press at MNRAS (small changes in section on neutrino detection

Application of Vector Spherical Harmonics and Kernel Regression to the computations of OMM Parameters

The high quality of Hipparcos data in position, proper motion, and parallax has allowed for studies about stellar kinematics with the aim of achieving a better physical understanding of our galaxy, based on accurate calculus of the Ogorodnikov-Milne model (OMM) parameters. The use of discrete least squares is the most common adjustment method, but it may lead to errors mainly because of the inhomogeneous spatial distribution of the data. We present an example of the instability of this method using the case of a function given by a linear combination of Legendre polynomials. These polynomials are basic in the use of vector spherical harmonics, which have been used to compute the OMM parameters by several authors, such as Makarov & Murphy, Mignard & Klioner, and Vityazev & Tsvetkov. To overcome the former problem, we propose the use of a mixed method (see Marco et al.) that includes the extension of the functions of residuals to any point on the celestial sphere. The goal is to be able to work with continuous variables in the calculation of the coefficients of the vector spherical harmonic developments with stability and efficiency. We apply this mixed procedure to the study of the kinematics of the stars in our Galaxy, employing the Hipparcos velocity field data to obtain the OMM parameters. Previously, we tested the method by perturbing the Vectorial Spherical Harmonics model as well as the velocity vector field.Part of this work was supported by a grant P1-1B2012-47 from UJI.Marco Castillo, FJ.; Martínez Uso, MJ.; Lopez, J. (2015). Application of Vector Spherical Harmonics and Kernel Regression to the computations of OMM Parameters. Astronomical Journal. 149(4):1-11. https://doi.org/10.1088/0004-6256/149/4/129S111149

Vertical distribution of Galactic disk stars IV - AMR and AVR from clump giants

We present the parameters of 891 stars, mostly clump giants, including atmospheric parameters, distances, absolute magnitudes, spatial velocities, galactic orbits and ages. One part of this sample consists of local giants, within 100 pc, with atmospheric parameters either estimated from our spectroscopic observations at high resolution and high signal-to-noise ratio, or retrieved from the literature. The other part of the sample includes 523 distant stars, which we have estimated atmospheric parameters from high resolution but low signal-to-noise Echelle spectra. This new sample is kinematically unbiased, with well-defined boundaries in magnitude and colours. We revisit the basic properties of the Galactic thin disk as traced by clump giants. We find the metallicity distribution to be different from that of dwarfs, with less metal-rich stars. We find evidence for a vertical metallicity gradient of -0.31 dex/kpc and for a transition at 4-5 Gyr in both the metallicity and velocities. The age - metallicity relation (AMR), which exhibits a very low dispersion, increases smoothly from 10 to 4 Gyr, with a steeper increase for younger stars. The age-velocity relation (AVR) is characterized by the saturation of the V and W dispersions at 5 Gyr, and continuous heating in U.Comment: 13 pages, 14 figures, accepted in A&

Global and Local Three-dimensional Studies of The Residual Vector Field from 2MASS and Hipparcos-2 Catalog

[EN] The Gaia mission will provide a six-parameter solution for millions of stars, including a tridimensional map of our Galaxy. The estimation of distances has been made for the Tycho-Gaia Astrometric Solution (TGAS), while to contrast the proper motions it is interesting to consider positions from the different Gaia Data Release with older ones given in ground-based massive catalogs. This process has been followed to build, for example, the PMA catalog using the 2MASS. Our aim is to improve the positions of this catalog (although the process is applicable to any other). The first stage, presented here, consists of carrying out a three-dimensional study using vector spherical harmonics (VSH) development of the systematisms in position for the stars common with Hipparcos-2; we take into account the distances, magnitudes, and spectral types. To this aim, we use linear polynomial regression of first order that fits vector fields and the derivatives of their components. We verify that the coefficients of the developments of first order have different behavior according to the characteristics of stars and distances. To deepen the study, we focus on the conservative component of the field, applying the Helmholtz theorem. Each potential function is obtained solving a Poisson equation on the sphere, after finding the divergence of the corresponding vector field. Both vector and potential fields present patterns, at certain points, that depend on the three considered parameters (distance, magnitude, and spectral type); their sources and shrinks correspond to maxima and minima. In this sense, we observe that these critical points are also critical points of the surface that represents the VT magnitude of Tycho-2, which makes sense because this catalog was used in the reduction of 2MASS positions. Finally, we selected some stars near the critical points of the vector fields and apply the adjustments obtained in the previous sections. The difference with the positions in DR1 allows us to compare the proper motions: those from the PMA and those induced after our corrections.This paper was partially supported by the UJI-B2016-18, 16I356 project.Marco Castillo, FJ.; Martínez Uso, MJ.; Lopez, J. (2019). Global and Local Three-dimensional Studies of The Residual Vector Field from 2MASS and Hipparcos-2 Catalog. Publications of the Astronomical Society of the Pacific. 131(998):1-22. https://doi.org/10.1088/1538-3873/aaed5dS122131998Akhmetov, V. S., Fedorov, P. N., Velichko, A. B., & Shulga, V. M. (2017). The PMA Catalogue: 420 million positions and absolute proper motions. Monthly Notices of the Royal Astronomical Society, 469(1), 763-773. doi:10.1093/mnras/stx812Arenou, F., Luri, X., Babusiaux, C., Fabricius, C., Helmi, A., Robin, A. C., … Bragaglia, A. (2017). Gaia Data Release 1. Astronomy & Astrophysics, 599, A50. doi:10.1051/0004-6361/201629895Astraatmadja, T. L., & Bailer-Jones, C. A. L. (2016). ESTIMATING DISTANCES FROM PARALLAXES. II. PERFORMANCE OF BAYESIAN DISTANCE ESTIMATORS ON AGAIA-LIKE CATALOGUE. The Astrophysical Journal, 832(2), 137. doi:10.3847/0004-637x/832/2/137Astraatmadja, T. L., & Bailer-Jones, C. A. L. (2016). ESTIMATING DISTANCES FROM PARALLAXES. III. DISTANCES OF TWO MILLION STARS IN THEGaiaDR1 CATALOGUE. The Astrophysical Journal, 833(1), 119. doi:10.3847/1538-4357/833/1/119Bailer-Jones, C. A. L. (2015). Estimating Distances from Parallaxes. Publications of the Astronomical Society of the Pacific, 127(956), 994-1009. doi:10.1086/683116Davies, G. R., Lund, M. N., Miglio, A., Elsworth, Y., Kuszlewicz, J. S., North, T. S. H., … Schofield, M. (2017). Using red clump stars to correct theGaiaDR1 parallaxes. Astronomy & Astrophysics, 598, L4. doi:10.1051/0004-6361/201630066Gontcharov, G. A. (2017). Systematic error of the Gaia DR1 TGAS parallaxes from data for the red giant clump. Astronomy Letters, 43(8), 545-558. doi:10.1134/s1063773717060044Jeffreys, S. H. 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J., Martínez, M. J., & López, J. A. (2013). Homogenization in compiling ICRF combined catalogs. Astronomy & Astrophysics, 558, A98. doi:10.1051/0004-6361/201321995Marco, F. J., Martínez, M. J., & López, J. A. (2015). APPLICATION OF VECTOR SPHERICAL HARMONICS AND KERNEL REGRESSION TO THE COMPUTATIONS OF OMM PARAMETERS. The Astronomical Journal, 149(4), 129. doi:10.1088/0004-6256/149/4/129Masry, E., & Jianqing Fan. (1997). Local Polynomial Estimation of Regression Functions for Mixing Processes. Scandinavian Journal of Statistics, 24(2), 165-179. doi:10.1111/1467-9469.00056Michalik, D., Lindegren, L., & Hobbs, D. (2015). TheTycho-Gaiaastrometric solution. Astronomy & Astrophysics, 574, A115. doi:10.1051/0004-6361/201425310Michalik, D., Lindegren, L., Hobbs, D., & Lammers, U. (2014). Joint astrometric solution of HIPPARCOS andGaia. Astronomy & Astrophysics, 571, A85. doi:10.1051/0004-6361/201424606Mignard, F., & Klioner, S. (2012). Analysis of astrometric catalogues with vector spherical harmonics. Astronomy & Astrophysics, 547, A59. doi:10.1051/0004-6361/201219927De Ridder, J., Molenberghs, G., Eyer, L., & Aerts, C. (2016). Asteroseismic versusGaiadistances: A first comparison. Astronomy & Astrophysics, 595, L3. doi:10.1051/0004-6361/201629799Roeser, S., Demleitner, M., & Schilbach, E. (2010). THE PPMXL CATALOG OF POSITIONS AND PROPER MOTIONS ON THE ICRS. COMBINING USNO-B1.0 AND THE TWO MICRON ALL SKY SURVEY (2MASS). The Astronomical Journal, 139(6), 2440-2447. doi:10.1088/0004-6256/139/6/2440Röser, S., Schilbach, E., Schwan, H., Kharchenko, N. V., Piskunov, A. E., & Scholz, R.-D. (2008). PPM-Extended (PPMX) – a catalogue of positions and proper motions. Astronomy & Astrophysics, 488(1), 401-408. doi:10.1051/0004-6361:200809775Schönrich, R., & Aumer, M. (2017). Assessing distances and consistency of kinematics in Gaia/TGAS. 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Prospecting environmental mycobacteria: combined molecular approaches reveal unprecedented diversity

Background: Environmental mycobacteria (EM) include species commonly found in various terrestrial and aquatic environments, encompassing animal and human pathogens in addition to saprophytes. Approximately 150 EM species can be separated into fast and slow growers based on sequence and copy number differences of their 16S rRNA genes. Cultivation methods are not appropriate for diversity studies; few studies have investigated EM diversity in soil despite their importance as potential reservoirs of pathogens and their hypothesized role in masking or blocking M. bovis BCG vaccine. Methods: We report here the development, optimization and validation of molecular assays targeting the 16S rRNA gene to assess diversity and prevalence of fast and slow growing EM in representative soils from semi tropical and temperate areas. New primer sets were designed also to target uniquely slow growing mycobacteria and used with PCR-DGGE, tag-encoded Titanium amplicon pyrosequencing and quantitative PCR. Results: PCR-DGGE and pyrosequencing provided a consensus of EM diversity; for example, a high abundance of pyrosequencing reads and DGGE bands corresponded to M. moriokaense, M. colombiense and M. riyadhense. As expected pyrosequencing provided more comprehensive information; additional prevalent species included M. chlorophenolicum, M. neglectum, M. gordonae, M. aemonae. Prevalence of the total Mycobacterium genus in the soil samples ranged from 2.3×107 to 2.7×108 gene targets g−1; slow growers prevalence from 2.9×105 to 1.2×107 cells g−1. Conclusions: This combined molecular approach enabled an unprecedented qualitative and quantitative assessment of EM across soil samples. Good concordance was found between methods and the bioinformatics analysis was validated by random resampling. Sequences from most pathogenic groups associated with slow growth were identified in extenso in all soils tested with a specific assay, allowing to unmask them from the Mycobacterium whole genus, in which, as minority members, they would have remained undetected

Deep imaging survey of the environment of Alpha Centauri - I. Adaptive optics imaging of Alpha Cen B with VLT-NACO

Context: Alpha Centauri is our closest stellar neighbor, at a distance of only 1.3 pc, and its two main components have spectral types comparable to the Sun. This is therefore a favorable target for an imaging search for extrasolar planets. Moreover, indications exist that the gravitational mass of Alpha Cen B is higher than its modeled mass, the difference being consistent with a substellar companion of a few tens of Jupiter masses. Aims: We searched for faint comoving companions to Alpha Cen B. As a secondary objective, we built a catalogue of the detected background sources. Methods: We used the NACO adaptive optics system of the VLT in the J, H, and Ks bands to search for companions to Alpha Cen B. This instrument allowed us to achieve a very high sensitivity to point-like sources, with a limiting magnitude of m\_Ks ~ 18 at 7" from the star. We complemented this data set with archival coronagraphic images from the HST-ACS instrument to obtain an accurate astrometric calibration. Results: Over the observed area, we did not detect any comoving companion to Alpha Cen B down to an absolute magnitude of 19-20 in the H and Ks bands. However, we present a catalogue of 252 background objects within about 15" of the star. This catalogue fills part of the large void area that surrounds Alpha Cen in sky surveys due to the strong diffused light. We also present a model of the diffused light as a function of angular distance for the NACO instrument, that can be used to predict the background level for bright star observations. Conclusions: According to recent numerical models, the limiting magnitude of our search sets the maximum mass of possible companions to 20-30 times Jupiter, between 7 and 20 AU from Alpha Cen B.Comment: 15 pages, accepted for publication in A&