The Real Estate Investment Trust: State Law Problems

We present a map of the three-dimensional (3D) distribution of dust in the Orion complex. Orion is the closest site of high-mass star formation, making it an excellent laboratory for studying the interstellar medium and star formation. We used data from the Gaia-TGAS catalogue combined with photometry from 2MASS and WISE to get the distances and extinctions of individual stars in the vicinity of the Orion complex. We use a Gaussian process and adopt a non-parametric method to infer the probability distribution function of the dust densities at arbitrary points throughout the region. We map the dust distribution towards different parts of the Orion complex. We find that the distance and depth of the cloud are compatible with other recent works, which show that the method can be applicable to local molecular clouds to map their 3D dust distribution. We also demonstrate the danger of only using colours of stars to derive their extinctions without considering further physical constraints, such as the colour-magnitude diagram (CMD)

Representing complex data using localized principal components with application to astronomical data

Often the relation between the variables constituting a multivariate data space might be characterized by one or more of the terms: ``nonlinear'', ``branched'', ``disconnected'', ``bended'', ``curved'', ``heterogeneous'', or, more general, ``complex''. In these cases, simple principal component analysis (PCA) as a tool for dimension reduction can fail badly. Of the many alternative approaches proposed so far, local approximations of PCA are among the most promising. This paper will give a short review of localized versions of PCA, focusing on local principal curves and local partitioning algorithms. Furthermore we discuss projections other than the local principal components. When performing local dimension reduction for regression or classification problems it is important to focus not only on the manifold structure of the covariates, but also on the response variable(s). Local principal components only achieve the former, whereas localized regression approaches concentrate on the latter. Local projection directions derived from the partial least squares (PLS) algorithm offer an interesting trade-off between these two objectives. We apply these methods to several real data sets. In particular, we consider simulated astrophysical data from the future Galactic survey mission Gaia.Comment: 25 pages. In "Principal Manifolds for Data Visualization and Dimension Reduction", A. Gorban, B. Kegl, D. Wunsch, and A. Zinovyev (eds), Lecture Notes in Computational Science and Engineering, Springer, 2007, pp. 180--204, http://www.springer.com/dal/home/generic/search/results?SGWID=1-40109-22-173750210-

Improving white dwarfs as chronometers with gaia parallaxes and spectroscopic metallicities

White dwarfs (WDs) offer unrealized potential in solving two problems in astrophysics: stellar age accuracy and precision. WD cooling ages can be inferred from surface temperatures and radii, which can be constrained with precision by high-quality photometry and parallaxes. Accurate and precise Gaia parallaxes along with photometric surveys provide information to derive cooling and total ages for vast numbers of WDs. Here we analyze 1372 WDs found in wide binaries with main-sequence (MS) companions and report on the cooling and total age precision attainable in these WD+MS systems. The total age of a WD can be further constrained if its original metallicity is known because the MS lifetime depends on metallicity at fixed mass, yet metallicity is unavailable via spectroscopy of the WD. We show that incorporating spectroscopic metallicity constraints from 38 wide binary MS companions substantially decreases internal uncertainties in WD total ages compared to a uniform constraint. Averaged over the 38 stars in our sample, the total (internal) age uncertainty improves from 21.04% to 16.77% when incorporating the spectroscopic constraint. Higher mass WDs yield better total age precision; for eight WDs with zero-age MS masses ≥2.0 M⊙, the mean uncertainty in total ages improves from 8.61% to 4.54% when incorporating spectroscopic metallicities. We find that it is often possible to achieve 5% total age precision for WDs with progenitor masses above 2.0 M⊙ if parallaxes with ≤1% precision and Pan-STARRS g, r, and i photometry with ≤0.01 mag precision are available

Spectral Classification; Old and Contemporary

Beginning with a historical account of the spectral classification, its refinement through additional criteria is presented. The line strengths and ratios used in two dimensional classifications of each spectral class are described. A parallel classification scheme for metal-poor stars and the standards used for classification are presented. The extension of spectral classification beyond M to L and T and spectroscopic classification criteria relevant to these classes are described. Contemporary methods of classifications based upon different automated approaches are introduced.Comment: To be published in "Principles and Perspectives in Cosmochemistry" Lecture Notes on Kodai School on Synthesis of Elements in Stars: Ed Aruna Goswami & Eswar Reddy, Springer Verlag, 2009, 17 pages, 10 figure

Balmer Filaments in Tycho's Supernova Remnant: An Interplay between Cosmic-ray and Broad-neutral Precursors

We present H alpha spectroscopic observations and detailed modeling of the Balmer filaments in the supernova remnant (SNR) Tycho (SN 1572). We used GH alpha FaS (Galaxy H alpha Fabry-Perot Spectrometer) on the William Herschel Telescope with a 3'.4 x 3'.4 field of view, 0 ''.2 pixel scale, and sigma(instr) = 8.1 km s(-1) resolution at 1 '' seeing for similar to 10. hr, resulting in 82 spatial-spectral bins that resolve the narrow H alpha line in the entire SN 1572 northeastern rim. For the first time, we can therefore mitigate artificial line broadening from unresolved differential motion and probe H alpha emission parameters in varying shock and ambient medium conditions. Broad H alpha line remains unresolved within spectral coverage of 392 km s-1. We employed Bayesian inference to obtain reliable parameter confidence intervals and to quantify the evidence for models with multiple line components. The median H alpha narrow-line (NL) FWHM of all bins and models is W-NL = (54.8 +/- 1.8) km s(-1) at the 95% confidence level, varying within [35, 72] km s(-1) between bins and clearly broadened compared to the intrinsic (thermal) approximate to 20 km s(-1). Possible line splits are accounted for, significant in approximate to 18% of the filament, and presumably due to remaining projection effects. We also find widespread evidence for intermediate-line emission of a broad-neutral precursor, with a median W-IL =(180 +/- 14) km s(-1) (95% confidence). Finally, we present a measurement of the remnant's systemic velocity, V-LSR = -34 km s(-1), and map differential line-of-sight motions. Our results confirm the existence and interplay of shock precursors in Tycho's remnant. In particular, we show that suprathermal NL emission is near-universal in SN 1572, and that, in the absence of an alternative explanation, collisionless SNR shocks constitute a viable acceleration source for Galactic TeV cosmic-ray protons

Surface features, rotation and atmospheric variability of ultra cool dwarfs

Photometric I band light curves of 21 ultra cool M and L dwarfs are presented. Variability with amplitudes of 0.01 to 0.055 magnitudes (RMS) with typical timescales of an hour to several hours are discovered in half of these objects. Periodic variability is discovered in a few cases, but interestingly several variable objects show no significant periods, even though the observations were almost certainly sensitive to the expected rotation periods. It is argued that in these cases the variability is due to the evolution of the surface features on timescales of a few hours. This is supported in the case of 2M1145 for which no common period is found in two separate light curves. It is speculated that these features are photospheric dust clouds, with their evolution possibly driven by rotation and turbulence. An alternative possibility is magnetically-induced surface features. However, chromospheric activity undergoes a sharp decrease between M7 and L1, whereas a greater occurrence of variability is observed in objects later than M9, lending support to the dust interpretation.Comment: To appear in "Ultracool Dwarf Stars" (Lecture Notes in Physics), H.R.A. Jones, I. Steele (eds), Springer-Verlag, 2001. Also available from http://www.mpia-hd.mpg.de/homes/calj/ultra.htm

An evolving jet from a strongly magnetized accreting X-ray pulsar

© 2018, Springer Nature Limited. Relativistic jets are observed throughout the Universe and strongly affect their surrounding environments on a range of physical scales, from Galactic binary systems1 to galaxies and clusters of galaxies2. All types of accreting black hole and neutron star have been observed to launch jets3, with the exception of neutron stars with strong magnetic fields4,5 (higher than 1012 gauss), leading to the conclusion that their magnetic field strength inhibits jet formation6. However, radio emission recently detected from two such objects could have a jet origin, among other possible explanations7,8, indicating that this long-standing idea might need to be reconsidered. But definitive observational evidence of such jets is still lacking. Here we report observations of an evolving jet launched by a strongly magnetized neutron star accreting above the theoretical maximum rate given by the Eddington limit. The radio luminosity of the jet is two orders of magnitude fainter than those seen in other neutron stars with similar X-ray luminosities9, implying an important role for the properties of the neutron star in regulating jet power. Our result also shows that the strong magnetic fields of ultra-luminous X-ray pulsars do not prevent such sources from launching jets

The Galactic warp revealed by Gaia DR2 kinematics

Using Gaia DR2  astrometry, we map the kinematic signature of the Galactic stellar warp out to a distance of 7 kpc from the Sun. Combining Gaia DR2  and 2-Micron All Sky Survey photometry, we identify, via a probabilistic approach, 599 494 upper main sequence (UMS) stars and 12 616 068 giants without the need for individual extinction estimates. The spatial distribution of the UMS stars clearly shows segments of the nearest spiral arms. The large-scale kinematics of both the UMS and giant populations show a clear signature of the warp of the Milky Way, apparent as a gradient of 5–6 km s⁻¹ in the vertical velocities from 8 to 14 kpc in Galactic radius. The presence of the signal in both samples, which have different typical ages, suggests that the warp is a gravitationally induced phenomenon

The kinematic signature of the Galactic warp with Gaia DR2

The second Gaia data release has published high-precision astrometric measurements for over a billion sources. In the coming years, Gaia data will make fundamental contributions to numerous open questions on the evolution of our Galaxy. We here focus on the long-standing debate on the origin and dynamical nature of the warp of our Galaxy, with particular attention to the warp-induced motions in stellar kinematics. Taking advantage of Gaia DR2 data, we detect the kinematic signature of the Galactic warp out to a distance of 7 kpc from the Sun. The signature manifests itself as a gradient of 5-6 km/s in the vertical velocities from 8 to 14 kpc in Galactic radius, with a signal-to-noise larger than 10. The signal is present in two samples of intrinsically young and old stellar populations, selected via a probabilistic approach. Based on our results, we argue that the warp is principally a gravitational phenomenon, thus placing an important constraint on the possible formation scenario. Finally, we observe that the old stellar populations present a smooth signal, as expected from a dynamically relaxed population, while the young sample exhibit a strongly perturbed kinematic pattern

Solid confirmation of the broad DIB around 864.8 nm using stacked Gaia–RVS spectra

Context. Studies of the correlation between different diffuse interstellar bands (DIBs) are important for exploring their origins. However, the Gaia–RVS spectral window between 846 and 870 nm contains few DIBs, the strong DIB at 862 nm being the only convincingly confirmed one. / Aims. Here we attempt to confirm the existence of a broad DIB around 864.8 nm and estimate its characteristics using the stacked Gaia–RVS spectra of a large number of stars. We study the correlations between the two DIBs at 862 nm (λ862) and 864.8 nm (λ864.8), as well as the interstellar extinction. / Methods. We obtained spectra of the interstellar medium (ISM) absorption by subtracting the stellar components using templates constructed from real spectra at high Galactic latitudes with low extinctions. We then stacked the ISM spectra in Galactic coordinates (ℓ,  b) – pixelized by the HEALPix scheme – to measure the DIBs. The stacked spectrum is modeled by the profiles of the two DIBs, Gaussian for λ862 and Lorentzian for λ864.8, and a linear continuum. We report the fitted central depth (CD), central wavelength, equivalent width (EW), and their uncertainties for the two DIBs. / Results. We obtain 8458 stacked spectra in total, of which 1103 (13%) have reliable fitting results after applying numerous conservative filters. This work is the first of its kind to fit and measure λ862 and λ864.8 simultaneously in cool-star spectra. Based on these measurements, we find that the EWs and CDs of λ862 and λ864.8 are well correlated with each other, with Pearson coefficients (rp) of 0.78 and 0.87, respectively. The full width at half maximum (FWHM) of λ864.8 is estimated as 1.62 ± 0.33 nm which compares to 0.55 ± 0.06 nm for λ862. We also measure the vacuum rest-frame wavelength of λ864.8 to be λ0 = 864.53 ± 0.14 nm, smaller than previous estimates. / Conclusions. We find solid confirmation of the existence of the DIB around 864.8 nm based on an exploration of its correlation with λ862 and estimation of its FWHM. The DIB λ864.8 is very broad and shallow. That at λ862 correlates better with E(BP − RP) than λ864.8. The profiles of the two DIBs could strongly overlap with each other, which contributes to the skew of the λ862 profile