118058418
Transit Timing Observations of the Extrasolar Hot‐Neptune Planet GL 436 b
Gliese 436 is an M dwarf with a mass of 0.45 M⊙ and hosts the extrasolar planet GL 436 b [3, 6, 7, 2], which is currently the least massive transiting planet with a mass of ∼23.17 M⊕ [10], and the only planet known to transit an M dwarf. GL 436 b represents the first transiting detection of the class of extrasolar planets known as “Hot Neptunes” that have masses within a few times that of Neptune’s mass (∼17 M⊕) and orbital semimajor axis <0.1 AU about the host star. Unlike most other known transiting extrasolar planets, GL 436 b has a high eccentricity (e∼0.16). This brings to light a new parameter space for habitability zones of extrasolar planets with host star masses much smaller than typical stars of roughly a solar mass. This unique system is an ideal candidate for orbital perturbation and transit‐time variation (TTV) studies to detect smaller, possibly Earth‐mass planets in the system. In April 2008 we began a long‐term intensive campaign to obtain complete high‐precision light curves using the Apa...
807139
Difference Image Analysis of Galactic Microlensing. I. Data Analysis
This is a preliminary report on the application of Difference Image Analysis (DIA) to Galactic bulge images. The aim of this analysis is to increase the sensitivity to the detection of gravitational microlensing. We discuss how the DIA technique simplifies the process of discovering microlensing events by detecting only objects that have variable flux. We illustrate how the DIA technique is not limited to detection of so-called ''pixel lensing'' events but can also be used to improve photometry for classical microlensing events by removing the effects of blending. We will present a method whereby DIA can be used to reveal the true unblended colors, positions, and light curves of microlensing events. We discuss the need for a technique to obtain the accurate microlensing timescales from blended sources and present a possible solution to this problem using the existing Hubble Space Telescope color-magnitude diagrams of the Galactic bulge and LMC. The use of such a solution with both classical and pixel microlensing searches is discussed. We show that one of the major causes of systematic noise in DIA is differential refraction. A technique for removing this systematic by effectively registering images to a common air mass is presented. Improvements to commonlymore » used image differencing techniques are discussed. (c) 1999 The American Astronomical Society.« less
118795031
Cepheid Variables in the LMC and SMC
In this paper, we will review major new results regarding classical Cepheids, in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC). Specifically, we discuss recent work regarding multimode Cepheids and describe new observations of a W Vir star (HV 5756) and a Cepheid which are each in eclipsing binary systems. An additional interesting pulsating supergiant in an eclipsing system is also identified. Ephemerides for eclipses for the three systems are provided.
9891842
The Peculiar Periodic YSO WL 4 in ρ Ophiuchus
We present the discovery of 130.87 day periodic near-infrared flux variability for the Class II T Tauri star WL 4 (=2MASS J16271848–2429059, ISO-Oph 128). Our data are from the 2MASS Calibration Point Source Working Database and constitute 1580 observations in J, H, and Ks of a field in ρ Ophiuchus used to calibrate the 2MASS All-Sky Survey. We identify a light curve for WL 4 with eclipse amplitudes of ~0.4 mag lasting more than one-quarter the period and color variations in J–H and H–Ks of ~0.1 mag. The long period cannot be explained by stellar rotation. We propose that WL 4 is a triple YSO system, with an inner binary orbital period of 130.87 days. We posulate that we are observing each component of the inner binary alternately being eclipsed by a circumbinary disk with respect to our line of sight. This system will be useful in investigating terrestrial-zone YSO disk properties and dynamics at ~1 Myr.
18048767
The Impact of the Astro2010 Recommendations on Variable Star Science
The next decade of survey astronomy has the potential to transform our knowledge of variable stars. Stellar variability underpins our knowledge of the cosmological distance ladder, and provides direct tests of stellar formation and evolution theory. Variable stars can also be used to probe the fundamental physics of gravity and degenerate material in ways that are otherwise impossible in the laboratory. The computational and engineering advances of the past decade have made large-scale, time-domain surveys an immediate reality. Some surveys proposed for the next decade promise to gather more data than in the prior cumulative history of astronomy. The actual implementation of these surveys will have broad implications for the types of science that will be enabled. We examine the design considerations for an optimal time-domain photometric survey dedicated to variable star science, including: observing cadence, wavelength coverage, photometric and astrometric accuracy, single-epoch and cumulative depth, overall sky coverage, and data access by the broader astronomical community. The best surveys must combine aspects from each of these considerations to fully realize the potential for the next decade of time-domain science.
9787512
The MACHO Project LMC Variable Star Inventory: Classical Cepheids, AGB Variables, and the Nine Million Star Color-Magnitude Diagram
We measure the ratio of ∼ 5M blue and red LMC supergiants (representative of classical Cepheids) using the MACHO Project’s 9 million star color-magnitude diagram (9M CMD) of the LMC bar. We find b/r = 0.39, which favors the z=0.008, 5M theoretical model of Schaerer et al. (1993) over that of Fagatto et al. (1994). Next, we examine the low mass (old) and low metallicity LMC field population (Pop. II). Features in the 9M CMD and properties of LMC field RRab variables are consistent with a mean iron abundance of [Fe/H] ≈ −1.5 dex for this population. Newly discovered post-HB/early-AGB Pop. II variables are identified in order to delineate the instability strip (IS). Good agreement with the theoretical IS of Bono et al. (1997) is found. We then compare the field RRab with newly identified RRab variables in the LMC clusters NGC 1898 and NGC 1835. We find the mean colors of these cluster RRab lie near the red and blue edges of the IS, respectively, which is similar to their respective (overall) red and blue HB morphologies. Since the field RRab lie on the red side of the IS, we infer the LMC field Pop. II is likely to have a red HB morphology.
43029702
Nuclear track registration in dosimeter glasses for neutron dosimetry in mixed radiation fields.
Abstract : The fission track detection in fission foil/glass combinations avoids most of the disadvantages of the conventional methods (nuclear track evaluations and activation foils) for integrating neutron measurements. These systems are insensitive to gamma radiation, temperature, climatic and chemical disturbances, easy to evaluate, have no directional dependence, an extended dose and energy range, superior accuracy, etc. The method has been investigated, using different dosimeter glasses, etching conditions, fissionable materials and neutron energies between thermal and 14 MeV. The fission track detection efficiency is 100%, the sensitivity for fissionable metals thicker than ca. 5 microns is 0.000013 tracks/neutron/barn. Simple evaluation techniques and practical applications, mainly for fast neutron personnel dosimetry, are described. (Author)
54769355
Scale-dependent non-Gaussianity as a generalization of the local model
We generalize the local model of primordial non-Gaussianity by promoting the parameter fNL to a general scale-dependent function fNL(k). We calculate the resulting bispectrum and the eect on the bias of dark matter halos, and thus the extent to which fNL(k) can be measured from the large-scale structure observations. By calculating the principal components of fNL(k), we identify scales where this form of non-Gaussianity is best constrained and estimate the overlap with previously studied local and equilateral non- Gaussian models.
18731427
Joint Minkowski functionals and bispectrum constraints on non-Gaussianity in the cosmic microwave background
Two of the most commonly used tools to constrain the primordial non-Gaussianity are the bispectrum and the Minkowski functionals of cosmic microwave background temperature anisotropies. These two measures of non-Gaussianity in principle provide distinct (though correlated) information, but in the past constraints from them have only been loosely compared and not statistically combined. In this work we evaluate, for the first time, the covariance matrix between the local non-Gaussianity coefficient ${f}_{\mathrm{NL}}$ estimated through the bispectrum and Minkowski functionals. We find that the estimators are positively correlated, with correlation coefficient $r\ensuremath{\simeq}0.3$. Using the WMAP7 data to combine the two measures and accounting for the point-source systematics, we find the combined constraint ${f}_{\mathrm{NL}}=37\ifmmode\pm\else\textpm\fi{}28$, which has a $\ensuremath{\sim}20%$ smaller error than either of the individual constraints.
10108151
First constraints on the running of non-Gaussianity.
We use data from the Wilkinson Microwave Anisotropy probe temperature maps to constrain a scale-dependent generalization of the popular "local" model for primordial non-Gaussianity. In the model where the parameter f(NL) is allowed to run with scale k, f(NL)(k) = f*(NL) (k/k(piv))(n)(fNL), we constrain the running to be n(f)(NL) = 0.30(-1.2)(+1.9) at 95% confidence, marginalized over the amplitude f*(NL). The constraints depend somewhat on the prior probabilities assigned to the two parameters. In the near future, constraints from a combination of Planck and large-scale structure surveys are expected to improve this limit by about an order of magnitude and usefully constrain classes of inflationary models.