scholarly journals Spectral mapping of V348 Puppis: spiral arms in the period gap★

2016 ◽  
Vol 457 (1) ◽  
pp. 198-211 ◽  
Author(s):  
R. K. Saito ◽  
R. Baptista
Keyword(s):  
Thermal Emission ◽  
Hubble Space Telescope ◽  
Accretion Disc ◽  
Spectral Mapping ◽  
Empirical Expression ◽  
Spiral Arms ◽  
Disc Centre ◽  
Angular Momentum Loss ◽  
Mapping Techniques ◽  
The Continuum

Abstract We report the analysis of Hubble Space Telescope (HST) UV–optical spectroscopy of the nova-like variable V348 Puppis with eclipse mapping techniques. We measured the eclipse width at disc centre and determined a lower limit on the mass ratio of q > 0.3, with a tight relation between q and the binary inclination i. For 0.31 ≤ q ≤ 0.6, we have 79$_{.}^{\circ}$5 ≤ i ≤ 88$_{.}^{\circ}$2. Simulations with 3D eclipse mapping give no support to the suggestion of self-shielding of the accretion disc of V348 Pup, indicating a geometrically thin disc. Eclipse maps reveal two structures in the accretion disc interpreted as tidally induced spiral arms, which account for 50–60  per cent of the disc flux in the continuum. The uneclipsed component accounts for 30–50  per cent of the light, indicating that a significant fraction of the light comes from a vertically extended disc chromosphere + wind. Its spectrum can be fitted by an isothermal slab of gas with temperature T = 9600 K and column density Σ ∼1010 g cm−2, corresponding to optically thick thermal emission. Superhumps had faded by the epoch of the HST observations; the disc shrank in size while the disc wind flux increased with respect to observations when superhumps were present. This may be explained if the disc wind outflow is the dominant source of angular momentum loss from the accretion disc. Previously observed accretion disc radii of V348 Pup and of two other binaries with large discs are used to derive an empirical expression for the maximum possible disc radius, which implies that superhumps may be found in systems with up to q ≃ 0.7.

scholarly journals Infrared photometry of the dwarf nova V2051 Ophiuchi – II. The quiescent accretion disc and its spiral arms

2019 ◽  
Vol 492 (1) ◽  
pp. 1154-1163 ◽  
Author(s):  
Raymundo Baptista ◽  
Eduardo Wojcikiewicz
Keyword(s):  
High Viscosity ◽  
Accretion Disc ◽  
Light Curves ◽  
Light Sources ◽  
Spiral Arms ◽  
Dwarf Nova ◽  
Wave Modulation ◽  
Disc Centre ◽  
Mapping Techniques ◽  
Analysis Of Time Series

ABSTRACT We report the analysis of time-series of infrared JHKs photometry of the dwarf nova  V2051 Oph in quiescence with eclipse mapping techniques to investigate structures and the spectrum of its accretion disc. The light curves after removal of the ellipsoidal variations caused by the mass-donor star show a double-wave modulation signalling the presence of two asymmetric light sources in the accretion disc. Eclipse maps reveal two spiral arms on top of the disc emission, one at $R_1= 0.28\pm 0.02 \, R_\mathrm{L1}$ and the other at $R_2= 0.42\pm 0.02 \, R_\mathrm{L1}$ (where RL1 is the distance from disc centre to the inner Lagrangian point), which are seen face-on at binary phases consistent with the maxima of the double-wave modulation. The wide open angle inferred for the spiral arms (θs = 21° ± 4°) suggests the quiescent accretion disc of V2051 Oph has high viscosity. The accretion disc is hot and optically thin in its inner regions ($T_\mathrm{gas}\sim 10\!-\!12 \times 10^3\, \mathrm{ K}$ and surface densities $\sim 10^{-3}\text{ to }10^{-2}\, \mathrm{ g}\, \mathrm{ cm}^{-2}$), and becomes cool and opaque in its outer regions.

scholarly journals A Strong Variation of Accretion Disc Corona Size with Luminosity in LMXB

2004 ◽  
Vol 194 ◽  
pp. 140-143
Author(s):  
M. J. Church
Keyword(s):  
Thermal Emission ◽  
Compact Object ◽  
Accretion Disc ◽  
Spectral Form ◽  
X Ray ◽  
Radial Extent ◽  
Low Mass ◽  
X Ray Binaries ◽  
Rule Out ◽  
The Continuum

AbstractThe controversy that has existed for many years over the nature of the continuum X-ray emission components in X-ray binaries is reviewed, in which workers have been polarized between the Eastern model with a small central Comptonizing region around the compact object and alternative models. We present measurements of the radial extent of the Comptonizing ADC in low mass X-ray binaries which rule out the Eastern model and show that, the ADC is extended (the Birmingham model). Dip ingress timing shows conclusively that the ADC radial extent varies from 7% of the accretion disc radius in faint sources, to 65% in bright sources. Remarkably, the size depends strongly on the source luminosity suggesting that the ADC is formed by irradiation of the disc by the neutron star and the hot inner disc. These results have fundamental implications for the correct description of Comptonization in X-ray binaries, and the spectral form is derived for the Comptonized emission of an extended ADC led by soft, seed photons from the underlying disc which differs substantially from that of the Eastern model. Measured ADC electron températures provide values of the Compton radius in broad agreement with measured values of the radial extent of the ADC. Finally, we show that the results are inconsistent with the non-thermal emission being produced in a jet, and so provide evidence against the recent suggestion that all LMXB have jets.

scholarly journals UV and X-ray observations of the neutron star LMXB EXO 0748–676 in its quiescent state

2020 ◽  
Vol 501 (1) ◽  
pp. 1453-1462
Author(s):  
A S Parikh ◽  
N Degenaar ◽  
J V Hernández Santisteban ◽  
R Wijnands ◽  
I Psaradaki ◽  
...  
Keyword(s):  
Neutron Star ◽  
Thermal Emission ◽  
Hubble Space Telescope ◽  
Dense Matter ◽  
Continuum Emission ◽  
Quiescent State ◽  
X Ray ◽  
Low Level ◽  
Low Mass ◽  
Different Origins

ABSTRACT The accretion behaviour in low-mass X-ray binaries (LMXBs) at low luminosities, especially at <1034 erg s−1, is not well known. This is an important regime to study to obtain a complete understanding of the accretion process in LMXBs, and to determine if systems that host neutron stars with accretion-heated crusts can be used probe the physics of dense matter (which requires their quiescent thermal emission to be uncontaminated by residual accretion). Here, we examine ultraviolet (UV) and X-ray data obtained when EXO 0748–676, a crust-cooling source, was in quiescence. Our Hubble Space Telescope spectroscopy observations do not detect the far-UV continuum emission, but do reveal one strong emission line, C iv. The line is relatively broad (≳3500 km s−1), which could indicate that it results from an outflow such as a pulsar wind. By studying several epochs of X-ray and near-UV data obtained with XMM–Newton, we find no clear indication that the emission in the two wavebands is connected. Moreover, the luminosity ratio of LX/LUV ≳ 100 is much higher than that observed from neutron star LMXBs that exhibit low-level accretion in quiescence. Taken together, this suggests that the UV and X-ray emission of EXO 0748–676 may have different origins, and that thermal emission from crust-cooling of the neutron star, rather than ongoing low-level accretion, may be dominating the observed quiescent X-ray flux evolution of this LMXB.

scholarly journals The Emission Spectrum of the Hot Jupiter WASP-79b from HST/WFC3

2021 ◽  
Vol 163 (1) ◽  
pp. 7
Author(s):  
Trevor O. Foote ◽  
Nikole K. Lewis ◽  
Brian M. Kilpatrick ◽  
Jayesh M. Goyal ◽  
Giovanni Bruno ◽  
...  
Keyword(s):  
Emission Spectrum ◽  
Energy Transport ◽  
Thermal Emission ◽  
Hubble Space Telescope ◽  
Vertical Mixing ◽  
Wide Field ◽  
Forward Models ◽  
Wide Range ◽  
Solar Metallicity ◽  
Recirculation Factor

Abstract Here we present a thermal emission spectrum of WASP-79b, obtained via Hubble Space Telescope Wide Field Camera 3 G141 observations as part of the PanCET program. As we did not observe the ingress or egress of WASP-79b’s secondary eclipse, we consider two scenarios: a fixed mid-eclipse time based on the expected occurrence time, and a mid-eclipse time as a free parameter. In both scenarios, we can measure thermal emission from WASP-79b from 1.1 to 1.7 μm at 2.4σ confidence consistent with a 1900 K brightness temperature for the planet. We combine our observations with Spitzer dayside photometry (3.6 and 4.5 μm) and compare these observations to a grid of atmospheric forward models that span a range of metallicities, carbon-to-oxygen ratios, and recirculation factors. Given the strength of the planetary emission and the precision of our measurements, we found a wide range of forward models to be consistent with our data. The best-match equilibrium model suggests that WASP-79b’s dayside has a solar metallicity and carbon-to-oxygen ratio, alongside a recirculation factor of 0.75. Models including significant H− opacity provide the best match to WASP-79b’s emission spectrum near 1.58 μm. However, models featuring high-temperature cloud species—formed via vigorous vertical mixing and low sedimentation efficiencies—with little day-to-night energy transport also match WASP-79b’s emission spectrum. Given the broad range of equilibrium chemistry, disequilibrium chemistry, and cloudy atmospheric models consistent with our observations of WASP-79b’s dayside emission, further observations will be necessary to constrain WASP-79b’s dayside atmospheric properties.

scholarly journals NGC 4258: A Bent Jet in a Spiral Galaxy

1982 ◽  
Vol 97 ◽  
pp. 145-147
Author(s):  
R. H. Sanders
Keyword(s):  
Spiral Galaxy ◽  
Leading Edge ◽  
Continuum Emission ◽  
Spiral Arms ◽  
Western Side ◽  
Normal Spiral ◽  
The Continuum

The remarkable continuum arms in the spiral galaxy NGC 4258 are suggestive of some form of ejection from the nucleus of this galaxy (Van der Kruit, Oort and Mathewson, 1972). To summarize the observations (see Oort, Figure 2, this volume), the “anomalous spiral arms” are clearly distinct from the normal spiral arms, although wound in the same sense; there is a sharp gradient of the continuum emission on the leading edge of the arms, and an indication that the arms split on the western side; the arms go directly into the nucleus and coincide with Hα emitting filaments (Courtes, Viton and Veron, 1965).

scholarly journals Multiwavelength characterization of the accreting millisecond X-ray pulsar and ultracompact binary IGR J17062–6143

2019 ◽  
Vol 488 (4) ◽  
pp. 4596-4606 ◽  
Author(s):  
J V Hernández Santisteban ◽  
V Cúneo ◽  
N Degenaar ◽  
J van den Eijnden ◽  
D Altamirano ◽  
...  
Keyword(s):  
Near Infrared ◽  
Thermal Emission ◽  
Spectral Energy Distribution ◽  
Mass Transfer Rate ◽  
Current Data ◽  
Accretion Disc ◽  
Spectral Energy ◽  
Companion Star ◽  
X Ray ◽  
Binary Evolution

ABSTRACT IGR J17062–6143 is an ultracompact X-ray binary (UCXB) with an orbital period of 37.96 min. It harbours a millisecond X-ray pulsar that is spinning at 163 Hz and and has continuously been accreting from its companion star since 2006. Determining the composition of the accreted matter in UCXBs is of high interest for studies of binary evolution and thermonuclear burning on the surface of neutron stars. Here, we present a multiwavelength study of IGR J17062–6143 aimed to determine the detailed properties of its accretion disc and companion star. The multi-epoch photometric UV to near-infrared spectral energy distribution (SED) is consistent with an accretion disc Fν ∝ ν1/3. The SED modelling of the accretion disc allowed us to estimate an outer disc radius of $R_{\rm out} = 2.2^{+0.9}_{-0.4} \times 10^{10}$ cm and a mass-transfer rate of $\dot{m} = 1.8^{+1.8}_{-0.5}\times 10^{-10}$ M⊙ yr−1. Comparing this with the estimated mass-accretion rate inferred from its X-ray emission suggests that ≳90 per cent of the transferred mass is lost from the system. Moreover, our SED modelling shows that the thermal emission component seen in the X-ray spectrum is highly unlikely from the accretion disc and must therefore represent emission from the surface of the neutron star. Our low-resolution optical spectrum revealed a blue continuum and no emission lines, i.e. lacking H and He features. Based on the current data we cannot conclusively identify the nature of the companion star, but we make recommendations for future study that can distinguish between the different possible evolution histories of this X-ray binary. Finally, we demonstrate how multiwavelength observations can be effectively used to find more UCXBs among the LMXBs.

A Refined Method of Parameterizing Absorption Coefficients among Multiple Gases Simultaneously from Line-by-Line Data

2005 ◽  
Vol 62 (2) ◽  
pp. 506-517 ◽  
Author(s):  
Mark Z. Jacobson
Keyword(s):  
Three Dimensional ◽  
Incident Radiation ◽  
Mapping Method ◽  
Atmospheric Models ◽  
Spectral Mapping ◽  
Absorption Coefficients ◽  
Distribution Method ◽  
Probability Interval ◽  
Irradiance Data ◽  
Mapping Techniques

Abstract An extension of the correlated-k distribution method that uses spectral-mapping techniques was derived to parameterize line-by-line absorption coefficients for multiple gases simultaneously for use in three-dimensional atmospheric models. In a variation from previous correlation techniques, this technique ensures exact correlation of absorption frequencies within a probability interval for all gases through all layers of the atmosphere when multiple gases are considered. The technique is physical since, in reality, gases are correlated in wavelength space. The technique, referred to as the “multiple-absorber correlated-k distribution spectral-mapping method,” was found to be accurate to <0.7% of incident radiation for 16 probability intervals per wavelength interval, integrated over 0.4–1000-μm wavelengths and accounting for 11 absorbing gases simultaneously and multiple layers, compared with an exact line-by-line solution. A method was also derived to reduce the number of probability intervals required for a radiative transfer solution without suffering the same inaccuracy as merely reducing the number of probability intervals when parameterizing the absorption coefficient. The new coefficients were tested in a global model, and results were compared with mean thermal-IR irradiance data.

A satellite perspective on jökulhlaups in Greenland

2012 ◽  
Vol 44 (1) ◽  
pp. 68-77 ◽  
Author(s):  
Morten Larsen ◽  
Christian Tøttrup ◽  
Eva Mätzler ◽  
Bo Naamansen ◽  
Dorthe Petersen ◽  
...  
Keyword(s):  
Bottom Topography ◽  
Gis Analysis ◽  
Spectral Mapping ◽  
Landsat Images ◽  
Glacial Ice ◽  
Surface Areas ◽  
Mapping Techniques ◽  
Remote Sensing Techniques ◽  
Landsat Satellite ◽  
Hydrological Station

Methods by remote sensing techniques were developed to locate potential jökulhlaup lakes and to assess the volume of water discharged. To locate potential jökulhlaup lakes, a time sequence of LandSat satellite imagery covering the area was investigated with spectral mapping techniques. The investigations showed how LandSat images can be used to map surface water, glacial ice, and surface temporal anomalies, and when combined with geographic information system (GIS) analysis, potential jökulhlaup lakes could be identified. For assessing the volume of the water discharged, the bottom topography for the jökulhlaup lakes were mapped from stereo images acquired by the ASTER satellite sensor and thereby defining the relations between the lake surface areas and the volumes of water stored in the lakes. Annual lake areas outlined from LandSat images were combined with the area-volume relations to describe the change over time in the volume of water in the lakes and thereby the volume released during jökulhlaups. The results of the volume assessments were validated against recordings from a hydrological station in the downstream lake. The validation underpinned the credibility of the method and as it relies on satellite data that are readily available, the method is applicable for use in many areas of the world.

scholarly journals The soft X-ray landscape of gamma-ray bursts: thermal components

2011 ◽  
Vol 7 (S279) ◽  
pp. 175-182
Author(s):  
Rhaana Starling ◽  
Kim Page ◽  
Martin Sparre
Keyword(s):  
Gamma Ray ◽  
Thermal Emission ◽  
Gamma Ray Bursts ◽  
Continuum Emission ◽  
Line Of Sight ◽  
X Ray ◽  
Multiple Components ◽  
The Standard Model ◽  
New Discovery ◽  
The Continuum

AbstractThe repository of GRB (gamma-ray burst) observations made by the Swift X-ray Telescope, now consisting of over 650 bursts, is a valuable and unique resource for the study of GRB X-ray emission. The observed soft X-ray spectrum typically arises from an underlying power law continuum, absorbed by gas along the line-of-sight. However, particularly at early times in a burst's evolution the continuum emission is not always understood and may comprise multiple components including thermal emission unexpected in the standard model. A thermal X-ray component has been discovered in two very unusual GRBs, perhaps suggesting an association only with this subset of events. However, evidence exists for thermal emission from more typical examples and here we present a new discovery of one such case and describe a systematic search for thermal components among all early GRB X-ray spectra.

scholarly journals A persistent ultraviolet outflow from the accretion disc in a transient neutron star binary

2021 ◽  
Author(s):  
Noel Castro Segura ◽  
Christian Knigge ◽  
Knox Long ◽  
Diego Altamirano ◽  
Montserrat Armas Padilla ◽  
...  
Keyword(s):  
Neutron Star ◽  
Hubble Space Telescope ◽  
Uv Spectroscopy ◽  
Accretion Disc ◽  
Absorption Lines ◽  
Time Resolved ◽  
X Ray ◽  
Astrophysical Objects ◽  
Hard State ◽  
The Impact

Abstract All disc-accreting astrophysical objects also produce powerful disc winds and/or jets. In compact binaries containing neutron stars or black holes, accretion often takes place during violent outbursts. The main disc wind signatures seen during these eruptions are blue-shifted X-ray absorption lines. However, these signatures are only observed during "soft states", when the accretion disc generates most of the luminosity. By contrast, optical wind-formed absorption lines have recently been detected in "hard states", when the luminosity is dominated by a hot corona. The relationship between these disc wind signatures is unknown, and no erupting compact binary has so far been observed to display wind-formed lines between the X-ray and optical bands, despite the many strong resonance transitions in this ultraviolet (UV) region of the spectrum. In turn, the impact of disc winds on the overall mass and energy budget of these systems remains a key open question. Here, we show that the transient neutron star X-ray binary Swift J1858.6-0814 exhibits wind-formed, blue-shifted absorption features associated with C IV, N V and He II in time-resolved, UV spectroscopy obtained with the Cosmic Origins Spectrograph on board the Hubble Space Telescope during a luminous hard state. In simultaneous ground-based observations, the optical H and He I lines also display transient blue-shifted absorption troughs. By decomposing our UV data into constant and flaring components, we demonstrate that the blue-shifted absorption is associated with the former, which implies that the outflow is always present. The joint presence of UV and optical wind features in the hard state reveals a multi-phase and/or spatially stratified evaporative outflow from the outer disc. This type of persistent mass loss across all accretion states has been predicted by radiation-hydrodynamic simulations and is required to account for the shorter-than-expected outburst durations.

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