120455459
Long-period variables in the Large Magellanic Cloud. II. Infrared photometry, spectral classification, AGB evolution, and spatial distribution
Infrared JHK photometry and visual spectra have been obtained for a large sample of long-period variables (LPVs) in the Large Magellanic Cloud (LMC). Various aspects of the asymptotic giant branch (AGB) evolution of LPVs are discussed using these data. The birth/death rate of LPVs of different ages in the LMC is compared with the birth rates of appropriate samples of planetary nebulas, clump stars, Cepheids, and OH/IR stars. It appears that there are much fewer large-amplitude LPVs per unit galactic stellar mass in the LMC than in the Galaxy. It is suggested that this may be due to the fact that the evolved intermediate-age AGB stars in the LMC often turn into carbon stars, which tend to have smaller pulsation amplitudes than M stars. There is also a major discrepancy between the number of LPVs in the LMC (and in the Galaxy) and the number predicted by the theories of AGB evolution, pulsation, and mass loss. A distance modulus to the LMC of 18.66 + or - 0.05 is derived by comparing the LMC LPVs with P about 200 days with the 47 Tucanae Mira variables in the (K, log P) plane. 64 refs.
119525918
The Extragalactic Distance Scale Key Project. VIII. The Discovery of Cepheids and a New Distance to NGC 3621 Using the Hubble Space Telescope
We report on the discovery of Cepheids in the field spiral galaxy NGC 3621, based on observations made with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope (HST). NGC 3621 is one of 18 galaxies observed as a part of the HST Key Project on the Extragalactic Distance Scale, which aims to measure the Hubble constant to 10% accuracy. Sixty-nine Cepheids with periods in the range 9-60 days were observed over 12 epochs using the F555W filter, and over four epochs using the F814W filter. The HST F555W and F814W data were transformed to the Johnson V and Kron-Cousins I magnitude systems, respectively. Photometry was performed using two independent packages, DAOPHOT II/ALLFRAME and DoPHOT. Period-luminosity relations in the V and I bands were constructed using 36 fairly isolated Cepheids present in our set of 69 variables. Extinction-corrected distance moduli relative to the LMC of 10.63 ? 0.09 and 10.56 ? 0.10 mag were obtained using the ALLFRAME and DoPHOT data, respectively. True distance moduli of 29.13 ? 0.18 and 29.06 ? 0.18 mag, corresponding to distances of 6.3 ? 0.7 and 6.1 ? 0.7 Mpc, were obtained by assuming values of ?0 = 18.50 ? 0.10 mag and E(V - I) = 0.13 mag for the distance modulus and reddening of the LMC, respectively.
119051790
The Hubble Space Telescope Extragalactic Distance Scale Key Project. X. The Cepheid Distance to NGC 7331
The distance to NGC 7331 has been derived from Cepheid variables observed with the Hubble Space Telescope (HST) WFPC2, as part of the Extragalactic Distance Scale Key Project. Multiepoch exposures in F555W ( ~V) and F814W ( ~I), with photometry derived independently from DoPHOT and DAOPHOT/ALLFRAME programs, were used to detect a total of 13 reliable Cepheids, with periods between 11 and 42 days. The relative distance moduli between NGC 7331 and the LMC, derived from the V and I magnitudes, imply an extinction to NGC 7331 of AV = 0.47 ± 0.15 mag and an extinction-corrected distance modulus to NGC 7331 of 30.89 ± 0.14 (random), equivalent to a distance of 15.1+1.0−0.9 Mpc. There are additional systematic uncertainties in the distance modulus of ±0.12 mag resulting from the calibration of the Cepheid period-luminosity relation and a systematic offset of +0.05 ± 0.04 mag if the metallicity correction inferred from the M101 results of Kennicutt et al. are applied.
120271826
OH/IR stars in the Magellanic Clouds
A sample of IRAS point sources in the Magellanic Clouds has been searched for 1612 MHz maser emission and for infrared emission at JHKL'. Six point sources, all in the LMC, are found to be OH masers while 19 have strong infrared emission typical of evolved giant and supergiant stars with dense circumstellar shells. Near-infrared monitoring over ∼1700 days has yielded pulsation periods for nine of the sources. All sources are classified as AGB stars, core helium burning supergiants or preplanetary nebulae according to pulsation amplitude, luminosity, and redness
15067001
The Hubble Constant from the HST Key Project on the Extragalactic Distance Scale
The final efforts of the HST Key Project on the Extragalactic Distance Scale are presented. Four distance indicators, the Surface Brightness Fluctuation method, the Fundamental Plane for early-type galaxies, the Tully-Fisher relation and the Type Ia Supernovae, are calibrated using Cepheid distances to galaxies within 25 Mpc. The calibration is then applied to distant samples reaching cz~10000 km/s and (in the case of SNIa) beyond. By combining the constraints imposed on the Hubble constant by the four distance indicators, we obtain H0 = 71+/-6 km/s/Mpc.
18509877
Golden Binaries for LISA: Robust Probes of Strong-Field Gravity
The space interferometer LISA will detect the gravitational wave (GW) signal from the inspiral, plunge and ringdown phases of massive black hole binary mergers at cosmological distances. From the inspiral waves, we will be able to measure the masses of the binaries’ members; from the ringdown waves, we will be able to measure the mass of the final merged remnant. A subset of detected events allow the identification of both the inspiral and the ringdown waveforms in a given source, and thus allow a measurement of the total mass-energy lost to GWs over the coalescence, MGW. We define “golden” binary mergers to be those with measurement errors on MGW likely to be small enough for a physically useful determination of MGW by LISA. A detailed sensitivity study, combined with simple black hole population models, suggests that a few golden binary mergers may be detected during a 3-year LISA mission lifetime. Any such mass deficit measurement would constitute a robust and valuable observational test of strong-field relativistic gravity. An extension of this concept to include spin measurements may allow a direct empirical test of the black hole area theorem. Subject headings: black hole physics – cosmology: theory – quasars: general – galaxies: active, nuclei, interactions – gravitation – relativity
14821200
RINGS AND BALLS
We examine the various linkings in space-time of “ball-like” and “ring-like” topological solitons in certain nonlinear sigma models in 2+1 and 3+1 dimensions. By going to theories where soliton overlaps are forbidden, these linkings become homotopically nontrivial and can be studied by investigating the topology of the corresponding configuration spaces. Our analysis reveals the existence of topological terms which give the linking number of the world tubes of distinct species of ball solitons in 2+1 dimensions, or which in 3+1 dimensions count the number of times a ball or ring soliton threads through the center of a ring of a different species. We explicitly construct these terms for our models, and generalize them to cases where soliton overlaps are no longer strictly forbidden so the terms are no longer purely topological. One of the (3+1)-dimensional theories we consider also has topological solitons which consist of two rings (of distinct species) linked in space.
26491766
Massive black-hole binary inspirals: results from the LISA parameter estimation taskforce
The LISA Parameter Estimation Taskforce was formed in September 2007 to provide the LISA Project with vetted codes, source distribution models and results related to parameter estimation. The Taskforce's goal is to be able to quickly calculate the impact of any mission design changes on LISA's science capabilities, based on reasonable estimates of the distribution of astrophysical sources in the universe. This paper describes our Taskforce's work on massive black-hole binaries (MBHBs). Given present uncertainties in the formation history of MBHBs, we adopt four different population models, based on (i) whether the initial black-hole seeds are small or large and (ii) whether accretion is efficient or inefficient at spinning up the holes. We compare four largely independent codes for calculating LISA's parameter-estimation capabilities. All codes are based on the Fisher-matrix approximation, but in the past they used somewhat different signal models, source parametrizations and noise curves. We show that once these differences are removed, the four codes give results in extremely close agreement with each other. Using a code that includes both spin precession and higher harmonics in the gravitational-wave signal, we carry out Monte Carlo simulations and determine the number of events that can be detected and accurately localized in our four population models.
16429904
Gravitational-wave confusion background from cosmological compact binaries: Implications for future terrestrial detectors
Increasing the sensitivity of a gravitational-wave (GW) detector improves our ability to measure the characteristics of detected sources. It also increases the number of weak signals that contribute to the data. Because GW detectors have nearly all-sky sensitivity, they can be subject to a confusion limit: Many sources which cannot be distinguished may be measured simultaneously, defining a stochastic noise floor to the sensitivity. For GW detectors operating at present and for their planned upgrades, the projected event rate is sufficiently low that we are far from the confusion-limited regime. However, some detectors currently under discussion may have large enough reach to binary inspiral that they enter the confusion-limited regime. In this paper, we examine the binary inspiral confusion limit for terrestrial detectors. We consider a broad range of inspiral rates in the literature, several planned advanced gravitational-wave detectors, and the highly advanced 'Einstein telescope' design. Though most advanced detectors will not be impacted by this limit, the Einstein telescope with a very low-frequency 'seismic wall' may be subject to confusion noise. At a minimum, careful data analysis will be require to separate signals which will appear confused. This result should be borne in mind when designing highly advanced futuremore » instruments.« less
18174177
Gravitational wave astronomy and cosmology
The first direct observation of gravitational waves' action upon matter has recently been reported by the BICEP2 experiment. Advanced ground-based gravitational-wave detectors are being installed. They will soon be commissioned, and then begin searches for high-frequency gravitational waves at a sensitivity level that is widely expected to reach events involving compact objects like stellar mass black holes and neutron stars. Pulsar timing arrays continue to improve the bounds on gravitational waves at nanohertz frequencies, and may detect a signal on roughly the same timescale as ground-based detectors. The science case for space-based interferometers targeting millihertz sources is very strong. The decade of gravitational-wave discovery is poised to begin. In this writeup of a talk given at the 2013 TAUP conference, we will briefly review the physics of gravitational waves and gravitational-wave detectors, and then discuss the promise of these measurements for making cosmological measurements in the near future.