Abstract
We derive relative proper motions of stars in the fields of the globular clusters M12, NGC 6362, M4, M55, M22, NGC 6752, NGC 3201, M30, M10, NGC 362, M5 and 47 Tucanae based on data ...collected between 1997 and 2015 with the 1-m Swope telescope of Las Campanas Observatory. We determine membership class and membership probability for over 446 000 objects, and show that these are efficient methods for separating field stars from members of the cluster. In particular, membership probabilities of variable stars and blue/yellow/red stragglers are determined. Finally, we find absolute proper motions for six globular clusters from our sample: M55, NGC 3201, M10, NGC 362, M5 and 47 Tuc. An electronic catalogue of the derived proper motions is publicly available via the internet.
We report the discovery of three extrasolar planets that transit their moderately bright (m
V= 12-13) host stars. WASP-44b is a 0.89-M
Jup planet in a 2.42-day orbit around a G8V star. WASP-45b is a ...1.03-M
Jup planet which passes in front of the limb of its K2V host star every 3.13 days. Weak Ca ii H&K emission seen in the spectra of WASP-45 suggests that the star is chromospherically active. WASP-46b is a 2.10-M
Jup planet in a 1.43-day orbit around a G6V star. Rotational modulation of the light curves of WASP-46 and weak Ca ii H&K emission in its spectra show the star to be photospherically and chromospherically active.
We imposed circular orbits in our analyses as the radial-velocity data are consistent with (near-)circular orbits, as could be expected from both empirical and tidal-theory perspectives for such short-period, ∼Jupiter-mass planets. We discuss the impact of fitting for eccentric orbits for such planets when not supported by the data. The derived planetary and stellar radii depend on the fitted eccentricity and these parameters inform intense theoretical efforts concerning tidal circularization and heating, bulk planetary composition and the observed systematic errors in planetary and stellar radii. As such, we recommend exercising caution in fitting the orbits of short-period, ∼Jupiter-mass planets with an eccentric model when there is no evidence of non-circularity.
We compare broad emission-line profiles and estimate line ratios for all major emission lines between Lyα and Hβ in a sample of six quasars. The sources were chosen with two criteria in mind: the ...existence of high-quality optical and ultraviolet spectra and the possibility of sampling the spectroscopic diversity in the 4D eigenvector 1 (4DE1) context. In the latter sense, each source occupies a region (bin) in the full width at half-maximum (FWHM)(Hβ) versus Fe iiopt strength plane that is significantly different from the others. High signal-to-noise ratio Hβ emission-line profiles are used as templates for modelling the other lines (Lyα, C ivλ1549, He iiλ1640, Al iiiλ1860, Si iiiλ1892 and Mg iiλ2800). We can adequately model all broad lines assuming the existence of three components distinguished by blueshifted, unshifted and redshifted centroids indicated as a blue component (BLUE), broad component (BC) and very broad component (VBC), respectively. BC (electron density ne∼ 1012 cm−3, ionization parameter U∼ 10−2 and column density Nc≳ 1023 cm−2) is present in almost all type-1 quasars and therefore corresponds most closely to the classical broad-line emitting region (the reverberating component). The bulk of Mg iiλ2800 and Fe ii emission also arises in this region. The BLUE emission (log ne∼ 10, log U∼−1 and log Nc < 23) arises in less optically thick gas; it is often thought to arise in an accretion disc wind. The least understood component involves the VBC (high ionization and large column density), which is found in no more than half (but almost all radio-loud) type-1 quasars and luminous Seyfert nuclei. It is perhaps the most distinguishing characteristic of quasars with FWHM (Hβ) ≳ 4000 km s−1 that belong to the so-called population B of our 4DE1 space. Population A quasars FWHM (Hβ) ≲ 4000 km s−1 are dominated by BC emission in Hβ and BLUE component emission in C ivλ1549 and other high ionization lines. 4DE1 appears to be the most useful current context for revealing and unifying spectral diversity in type-1 quasars.
We present optical and near-infrared (NIR) photometry and spectroscopy as well as modelling of the lightcurves of the Type IIb supernova (SN) 2011dh. Our extensive dataset, for which we present the ...observations obtained after day 100, spans two years, and complemented with Spitzer mid-infrared (MIR) data, we use it to build an optical-to-MIR bolometric lightcurve between days 3 and 732. To model the bolometric lightcurve before day 400 we use a grid of hydrodynamical SN models, which allows us to determine the errors in the derived quantities, and a bolometric correction determined with steady-state non-local thermodynamic equilibrium (NLTE) modelling. Using this method we find a helium core mass of 3.1+0.7-0.4 M⊙ for SN 2011dh, consistent within error bars with previous results obtained using the bolometric lightcurve before day 80. We compute bolometric and broad-band lightcurves between days 100 and 500 from spectral steady-state NLTE models, presented and discussed in a companion paper. The preferred 12 M⊙ (initial mass) model, previously found to agree well with the observed spectra, shows a good overall agreement with the observed lightcurves, although some discrepancies exist. Time-dependent NLTE modelling shows that after day ~600 a steady-state assumption is no longer valid. The radioactive energy deposition in this phase is likely dominated by the positrons emitted in the decay of 56Co, but seems insufficient to reproduce the lightcurves, and what energy source is dominating the emitted flux is unclear. We find an excess in the K and the MIR bands developing between days 100 and 250, during which an increase in the optical decline rate is also observed. A local origin of the excess is suggested by the depth of the He i 20 581 Å absorption. Steady-state NLTE models with a modest dust opacity in the core (τ = 0.44), turned on during this period, reproduce the observed behaviour, but an additional excess in the Spitzer 4.5 μm band remains. Carbon-monoxide (CO) first-overtone band emission is detected at day 206, and possibly at day 89, and assuming the additional excess to bedominated by CO fundamental band emission, we find fundamental to first-overtone band ratios considerably higher than observed in SN 1987A. The profiles of the O i 6300 Å and Mg i 4571 Å lines show a remarkable similarity, suggesting that these lines originate from a common nuclear burning zone (O/Ne/Mg), and using small scale fluctuations in the line profiles we estimate a filling factor of ≲0.07 for the emitting material. This paper concludes our extensive observational and modelling work on SN 2011dh. The results from hydrodynamical modelling, steady-state NLTE modelling, and stellar evolutionary progenitor analysis are all consistent, and suggest an initial mass of ~12 M⊙ for the progenitor.
Stellar mergers are common Kochanek, C. S; Adams, Scott M; Belczynski, Krzysztof
Monthly notices of the Royal Astronomical Society,
09/2014, Letnik:
443, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The observed Galactic rate of stellar mergers or the initiation of common envelope phases brighter than M
V
= −3 (M
I
= −4) is of the order of ∼0.5 (0.3) yr−1 with 90 per cent confidence ...statistical uncertainties of 0.24–1.1 (0.14–0.65) and factor of ∼2 systematic uncertainties. The (peak) luminosity function is roughly
$\text{d}N/\text{d} L \propto L^{-1.4\pm 0.3}$
, so the rates for events more luminous than V1309 Sco (M
V
≃ −7 mag) or V838 Mon (M
V
≃ −10 mag) are lower at r ∼ 0.1 and ∼0.03/year, respectively. The peak luminosity is a steep function of progenitor mass, L ∝ M
2 − 3. This very roughly parallels the scaling of luminosity with mass on the main sequence, but the transients are ∼2000–4000 times more luminous at peak. Combining these, the mass function of the progenitors, dN/dM ∝ M
−2.0 ± 0.8, is consistent with the initial mass function, albeit with broad uncertainties. These observational results are also broadly consistent with the estimates of binary population synthesis models. While extragalactic variability surveys can better define the rates and properties of the high-luminosity events, systematic, moderate depth (I ≳ 16 mag) surveys of the Galactic plane are needed to characterize the low-luminosity events. The existing Galactic samples are only ∼20 per cent complete, and Galactic surveys are (at best!) reaching a typical magnitude limit of ≲ 13 mag.
We study the four BL Lac objects (RGB J0152+017, 1ES 0229+200, 1ES 0347−121 and PKS 0548−322) detected in the TeV band but not present in the first Fermi-LAT (1FGL) catalogue of the Fermi/Large Area ...Telescope (LAT). We analyse the 24 months of LAT data deriving γ-ray fluxes or upper limits that we use to assemble their spectral energy distributions (SED). We model the SEDs with a standard one-zone leptonic model, also including the contribution of the reprocessed radiation in the multi-GeV band, emitted by the pairs produced through the conversion of the primary TeV emission by interaction with the cosmic optical-infrared background. For simplicity, in the calculation of this component we adopt an analytical approach including some simplifying assumptions, in particular (i) the blazar high-energy emission is considered on average stable over times of the order of 107 yr and (ii) the observer is exactly on-axis. We compare the physical parameters derived by the emission model with those of other high-energy emitting BL Lacs, confirming that TeV BL Lacs with a rather small GeV flux are characterized by extremely low values of the magnetic field and large values of the electron energies. The comparison between the flux in the GeV band and that expected from the reprocessed TeV emission allows us to confirm and strengthen the lower limit of B≳ 10−15 G for the intergalactic magnetic field using a theoretically motivated spectrum for the primary high-energy photons.
We performed a systematic analysis of all INTEGRAL observations from 2003 to 2009 of 14 supergiant fast X-ray transients (SFXTs), implying a net exposure time of about 30 Ms. For each source we ...obtained light curves and spectra (3–100 keV), discovering several new outbursts. We discuss the X-ray behaviour of SFXTs emerging from our analysis in the framework of the clumpy wind accretion mechanism we proposed. We discuss the effect of X-ray photoionization on accretion in close binary systems such as IGR J16479−4514 and IGR J17544−2619. We show that, because of X-ray photoionization, there is a high probability of an accretion disc forming from the capture of angular momentum in IGR J16479−4514, and we suggest that the formation of transient accretion discs could be partly responsible for the flaring activity in SFXTs with narrow orbits. We also propose an alternative way to explain the origin of flares with peculiar shapes observed in our analysis applying the model of Lamb et al., which is based on accretion via the Rayleigh–Taylor instability and was originally proposed to explain Type II bursts.
Abstract
Gamma-ray bursts are thought to be sites of hadronic acceleration, thus neutrinos are expected from the decay of charged particles, produced in pγ interactions. The methods and results of a ...search for muon neutrinos in the data of the ANTARES neutrino telescope from four bright GRBs (GRB 080916C, GRB 110918A, GRB 130427A and GRB 130505A) observed between 2008 and 2013 are presented. Two scenarios of the fireball model have been investigated: the internal shock scenario, leading to the production of neutrinos with energies mainly above 100 TeV, and the photospheric scenario, characterized by a low-energy component in neutrino spectra due to the assumption of neutrino production closer to the central engine. Since no neutrino events have been detected in temporal and spatial coincidence with these bursts, upper limits at 90 per cent confidence level on the expected neutrino fluxes are derived. The non-detection allows for directly constraining the bulk Lorentz factor of the jet Γ and the baryon loading fp.
Extending over three Hubble Space Telescope (HST) cycles, the Hubble Frontier Fields (HFF) initiative constitutes the largest commitment ever of HST time to the exploration of the distant Universe ...via gravitational lensing by massive galaxy clusters. Here, we present models of the mass distribution in the six HFF cluster lenses, derived from a joint strong- and weak-lensing analysis anchored by a total of 88 multiple-image systems identified in existing HST data. The resulting maps of the projected mass distribution and of the gravitational magnification effectively calibrate the HFF clusters as gravitational telescopes. Allowing the computation of search areas in the source plane, these maps are provided to the community to facilitate the exploitation of forthcoming HFF data for quantitative studies of the gravitationally lensed population of background galaxies. Our models of the gravitational magnification afforded by the HFF clusters allow us to quantify the lensing-induced boost in sensitivity over blank-field observations and predict that galaxies at z > 10 and as faint as m(AB) = 32 will be detectable, up to 2 mag fainter than the limit of the Hubble Ultra Deep Field.
We present new data for five underluminous Type II-plateau supernovae (SNe IIP), namely SN 1999gn, SN 2002gd, SN 2003Z, SN 2004eg and SN 2006ov. This new sample of low-luminosity SNe IIP (LL SNe IIP) ...is analysed together with similar objects studied in the past. All of them show a flat light-curve plateau lasting about 100 d, an underluminous late-time exponential tail, intrinsic colours that are unusually red, and spectra showing prominent and narrow P Cygni lines. A velocity of the ejected material below 103 km s−1 is inferred from measurements at the end of the plateau. The 56Ni masses ejected in the explosion are very small (≤10−2 M). We investigate the correlations among 56Ni mass, expansion velocity of the ejecta and absolute magnitude in the middle of the plateau, confirming the main findings of Hamuy, according to which events showing brighter plateau and larger expansion velocities are expected to produce more 56Ni. We propose that these faint objects represent the LL tail of a continuous distribution in parameters space of SNe IIP. The physical properties of the progenitors at the explosion are estimated through the hydrodynamical modelling of the observables for two representative events of this class, namely SN 2005cs and SN 2008in. We find that the majority of LL SNe IIP, and quite possibly all, originate in the core collapse of intermediate-mass stars, in the mass range 10-15 M.
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