Taking the Measure of the Universe: Precision Astrometry with SIM PlanetQuest

Precision astrometry at microarcsecond accuracy has application to a wide range of astrophysical problems. This paper is a study of the science questions that can be addressed using an instrument that delivers parallaxes at about 4 microarcsec on targets as faint as V = 20, differential accuracy of 0.6 microarcsec on bright targets, and with flexible scheduling. The science topics are drawn primarily from the Team Key Projects, selected in 2000, for the Space Interferometry Mission PlanetQuest (SIM PlanetQuest). We use the capabilities of this mission to illustrate the importance of the next level of astrometric precision in modern astrophysics. SIM PlanetQuest is currently in the detailed design phase, having completed all of the enabling technologies needed for the flight instrument in 2005. It will be the first space-based long baseline Michelson interferometer designed for precision astrometry. SIM will contribute strongly to many astronomical fields including stellar and galactic astrophysics, planetary systems around nearby stars, and the study of quasar and AGN nuclei. SIM will search for planets with masses as small as an Earth orbiting in the `habitable zone' around the nearest stars using differential astrometry, and could discover many dozen if Earth-like planets are common. It will be the most capable instrument for detecting planets around young stars, thereby providing insights into how planetary systems are born and how they evolve with time. SIM will observe significant numbers of very high- and low-mass stars, providing stellar masses to 1%, the accuracy needed to challenge physical models. Using precision proper motion measurements, SIM will probe the galactic mass distribution and the formation and evolution of the Galactic halo. (abridged)Comment: 54 pages, 28 figures, uses emulateapj. Submitted to PAS

The globular cluster NGC 2419: a crucible for theories of gravity

We present the analysis of a kinematic data set of stars in the globular cluster NGC 2419, taken with Keck/DEIMOS. Combined with a reanalysis of deep HST and Subaru imaging data, which provide an accurate luminosity profile of the cluster, we investigate the validity of a large set of dynamical models of the system, which are checked for stability via N-body simulations. We find that isotropic models in either Newtonian or Modified Newtonian Dynamics (MOND) are ruled out with extremely high confidence. However, a simple Michie model in Newtonian gravity with anisotropic velocity dispersion provides an excellent representation of the luminosity profile and kinematics. In contrast, with MOND we find that Michie models that reproduce the luminosity profile either over-predict the velocity dispersion on the outskirts of the cluster if the mass to light ratio is kept at astrophysically-motivated values, or else they under-predict the central velocity dispersion if the mass to light ratio is taken to be very small. We find that the best Michie model in MOND is a factor of 10000 less likely than the Newtonian model that best fits the system. A likelihood ratio of 350 is found when we investigate more general models by solving the Jeans equation with a Markov-Chain Monte Carlo scheme. We verified with N-body simulations that these results are not significantly different when the MOND external field effect is accounted for. If the assumptions that the cluster is in dynamical equilibrium, spherical, not on a peculiar orbit, and possesses a single dynamical tracer population of constant M/L are correct, we conclude that the present observations provide a very severe challenge for MOND. [abridged]Comment: 25 pages, 19 figures, accepted for publication in Ap

The satellite distribution of M31

(Abridged) The spatial distribution of the Galactic satellite system plays an important role in Galactic dynamics and cosmology, where its successful reproduction is a key test of simulations of galaxy halo formation. Here, we examine its representative nature by conducting an analysis of the 3-dimensional spatial distribution of the M31 subgroup of galaxies. We begin by a discussion of distance estimates and incompleteness concerns, before revisiting the question of membership of the M31 subgroup. Comparison of the distribution of M31 and Galactic satellites relative to the galactic disks suggests that the Galactic system is probably modestly incomplete at low latitudes by ~20%. We find that the radial distribution of satellites around M31 is more extended than the Galactic subgroup; 50% of the Galactic satellites are found within ~100kpc of the Galaxy, compared to ~200kpc for M31. We search for ``ghostly streams'' of satellites around M31, in the same way others have done for the Galaxy, and find several. The lack of M31-centric kinematic data, however, means we are unable to probe whether these streams represent real physical associations. Finally, we find that the M31 satellites are asymmetrically distributed with respect to our line-of-sight to this object, so that the majority of its satellites are on its near side with respect to our line-of-sight. We quantify this result and find it to be significant at the ~3 sigma level. Until such time as a satisfactory explanation for this finding is presented, our results warn against treating the M31 subgroup as complete, unbiased and relaxed.Comment: 15 pages, 9 figures. Accepted for publication in MNRA

LSST Science Book, Version 2.0

A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of the exciting science opportunities of the next decade. The Large Synoptic Survey Telescope (LSST) will have an effective aperture of 6.7 meters and an imaging camera with field of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over 20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a total point-source depth of r~27.5. The LSST Science Book describes the basic parameters of the LSST hardware, software, and observing plans. The book discusses educational and outreach opportunities, then goes on to describe a broad range of science that LSST will revolutionize: mapping the inner and outer Solar System, stellar populations in the Milky Way and nearby galaxies, the structure of the Milky Way disk and halo and other objects in the Local Volume, transient and variable objects both at low and high redshift, and the properties of normal and active galaxies at low and high redshift. It then turns to far-field cosmological topics, exploring properties of supernovae to z~1, strong and weak lensing, the large-scale distribution of galaxies and baryon oscillations, and how these different probes may be combined to constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at http://www.lsst.org/lsst/sciboo

XHIP-II: Clusters and associations

Context. In the absence of complete kinematic data it has not previously been possible to furnish accurate lists of member stars for all moving groups. There has been an unresolved dispute concerning the apparent inconsistency of the Hipparcos parallax distance to the Pleiades. Aims. To find improved candidate lists for clusters and associations represented among Hipparcos stars, to establish distances, and to cast light on the Pleiades distance anomaly. Methods. We use a six dimensional fitting procedure to identify candidates, and plot CMDs for 20 of the nearest groups. We calculate the mean parallax distance for all groups. Results. We identify lists of candidates and calculated parallax distances for 42 clusters and 45 associations represented within the Hipparcos catalogue. We find agreement between parallax distance and photometric distances for the most important clusters. For single stars in the Pleiades we find mean parallax distance 125.6 \pm 4.2 pc and photometric distance 132 \pm 3 pc calibrated to nearby groups of similar in age and composition. This gives no reason to doubt either the Hipparcos database or stellar evolutionary theory.Comment: Accepted for publication in Astronomy Letters, 10 pages, 2 fig

The generalized F-statistic: multiple detectors and multiple GW pulsars

The F-statistic, derived by Jaranowski, Krolak & Schutz (1998), is the optimal (frequentist) statistic for the detection of nearly periodic gravitational waves from known neutron stars, in the presence of stationary, Gaussian detector noise. The F-statistic was originally derived for the case of a single detector, whose noise spectral density was assumed constant in time, and for a single known neutron star. Here we show how the F-statistic can be straightforwardly generalized to the cases of 1) a network of detectors with time-varying noise curves, and 2) a population of known sources. Fortunately, all the important ingredients that go into our generalized F-statistics are already calculated in the single-source/single-detector searches that are currently implemented, e.g., in the LIGO Software Library, so implementation of optimal multi-detector, multi-source searches should require negligible additional cost in computational power or software development.Comment: 6 pages, 0 figures, submitted to PRD; section IV substantially enlarged and revised, and a few typos correcte

A Mock Data Challenge for the Einstein Gravitational-Wave Telescope

Einstein Telescope (ET) is conceived to be a third generation gravitational-wave observatory. Its amplitude sensitivity would be a factor ten better than advanced LIGO and Virgo and it could also extend the low-frequency sensitivity down to 1--3 Hz, compared to the 10--20 Hz of advanced detectors. Such an observatory will have the potential to observe a variety of different GW sources, including compact binary systems at cosmological distances. ET's expected reach for binary neutron star (BNS) coalescences is out to redshift $z\simeq 2$ and the rate of detectable BNS coalescences could be as high as one every few tens or hundreds of seconds, each lasting up to several days. %in the sensitive frequency band of ET. With such a signal-rich environment, a key question in data analysis is whether overlapping signals can be discriminated. In this paper we simulate the GW signals from a cosmological population of BNS and ask the following questions: Does this population create a confusion background that limits ET's ability to detect foreground sources? How efficient are current algorithms in discriminating overlapping BNS signals? Is it possible to discern the presence of a population of signals in the data by cross-correlating data from different detectors in the ET observatory? We find that algorithms currently used to analyze LIGO and Virgo data are already powerful enough to detect the sources expected in ET, but new algorithms are required to fully exploit ET data.Comment: accepted for publication in Physical Review D -- 18 pages, 8 figure