Physical Interpretation of Dwarf Nova Primary Effective Temperatures

AbstractWe have undertaken a theoretical study of the impact of the accumulating envelopes on the thermal state of the underlying white dwarf (WD). This has allowed us to find the equilibrium WD core temperatures, the classical nova ignition masses and the thermal luminosities for WDs accreting at rates of 10–11 – 10–8M⊙ yr–1. These accretion rates are most, appropriate to WDs in cataclysmic variables (CVs) of (Porb ≲ 7 hr), many of which accrete sporadically as Dwarf Novae. Over twenty Dwarf Novae have been observed in quiescence, when the accretion rate is low and the WD photosphere is detected and Teff measured. Comparing our theoretical work to these observations allows us to constrain the WD mass and the time averaged accretion rate, ⟨Ṁ⟩. If ⟨Ṁ⟩ is that given by gravitational radiation losses alone, then the WD masses are > 0.8 M⊙. An alternative conclusion is that the masses are closer to 0.6M⊙ and ⟨Ṁ⟩ is 3-4 times larger than that expected from gravitational radiation losses.

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Thermal state of transiently accreting neutron stars with additional heating beyond deep crustal heating

Progress of Theoretical and Experimental Physics ◽

10.1093/ptep/ptaa029 ◽

2020 ◽

Vol 2020 (4) ◽

Author(s):

Helei Liu ◽

Masa-aki Hashimoto ◽

Guoliang Lü ◽

Yasuhide Matsuo ◽

Dehua Wen ◽

...

Keyword(s):

Neutron Star ◽

Heat Source ◽

Neutron Stars ◽

High Temperatures ◽

Accretion Rate ◽

Thermal State ◽

X Ray ◽

Mass Accretion Rate ◽

Accretion Rates ◽

Theoretical Predictions

Abstract As some neutron star transients require an additional unknown heat source (referred to as “shallow heating”) to explain their high temperatures at the beginning of quiescence, we investigate the effect of shallow heating as well as compressional heating on the thermal state of transiently accreting neutron stars with the use of evolutionary calculations in the present work. Through comparing our theoretical predictions of the equilibrium redshifted luminosities $(L_{\gamma}^{\infty})$ produced by both deep crustal heating and shallow heating/compressional heating for different time-averaged mass-accretion rates $\langle\dot{M}\rangle$ with 35 updated observations of soft X-ray transients, the results show that both shallow heating and compressional heating make significant contributions to the equilibrium redshifted luminosity. The hotter sources (XTE J1701, MAXI J0556, EXO 0748, Aql X-1 etc.) with higher accretion rates are more likely to be explained with the effect of shallow heating or compressional heating. In addition, for a proper shallow heat $q_\mathrm{sh}$ and mass-accretion rate $\dot{M}$, the effect of shallow heating could be simulated by compressional heating.

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Optical spectra of FO Aquarii during low and high accretion rates

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1415 ◽

2020 ◽

Vol 495 (4) ◽

pp. 4445-4462

Author(s):

M R Kennedy ◽

P M Garnavich ◽

C Littlefield ◽

T R Marsh ◽

P Callanan ◽

...

Keyword(s):

Transfer Rate ◽

Mass Transfer Rate ◽

Cataclysmic Variables ◽

Accretion Disc ◽

High State ◽

Secondary Star ◽

Accretion Rates ◽

Magnetic Poles ◽

The Impact ◽

Impact Region

ABSTRACT Between 2016 May and 2018 September, the intermediate polar (IP) FO Aquarii exhibited two distinct low states and one failed low state. We present optical spectroscopy of FO Aquarii throughout this period, making this the first detailed study of an accretion disc during a low state in any IP. Analysis of these data confirm that the low states are the result of a drop in the mass transfer rate between the secondary star and the magnetic white dwarf primary, and are characterized by a decrease in the system’s brightness coupled with a change of the system’s accretion structures from an accretion disc-fed geometry to a combination of disc-fed and ballistic stream-fed accretion, and that effects from accretion on to both magnetic poles become detectable. The failed low state only displays a decrease in brightness, with the accretion geometry remaining primarily disc-fed. We also find that the WD appears to be exclusively accretion disc-fed during the high state. There is evidence for an outflow close to the impact region between the ballistic stream and the disc which is detectable in all of the states. Finally, there is marginal evidence for narrow high-velocity features in the H α emission line during the low states which may arise due to an outflow from the WD. These features may be evidence of a collimated jet, a long predicted yet elusive feature of cataclysmic variables.

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AGNs at the cosmic dawn: predictions for future surveys from a ΛCDM cosmological model

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa024 ◽

2020 ◽

Vol 492 (2) ◽

pp. 2535-2552

Author(s):

Andrew J Griffin ◽

Cedric G Lacey ◽

Violeta Gonzalez-Perez ◽

Claudia del P Lagos ◽

Carlton M Baugh ◽

...

Keyword(s):

Black Holes ◽

Galaxy Formation ◽

Near Infrared ◽

Accretion Rate ◽

High Redshift ◽

Host Galaxies ◽

Accretion Rates ◽

Infrared Wavelengths ◽

The Masses ◽

High Redshift Universe

ABSTRACT Telescopes to be launched over the next decade and a half, such as JWST, EUCLID, ATHENA, and Lynx, promise to revolutionize the study of the high-redshift Universe and greatly advance our understanding of the early stages of galaxy formation. We use a model that follows the evolution of the masses and spins of supermassive black holes (SMBHs) within a semi-analytic model of galaxy formation to make predictions for the active galactic nucleus luminosity function at $z$ ≥ 7 in the broadband filters of JWST and EUCLID at near-infrared wavelengths, and ATHENA and Lynx at X-ray energies. The predictions of our model are relatively insensitive to the choice of seed black hole mass, except at the lowest luminosities (Lbol < 1043 erg s−1) and the highest redshifts ($z$ > 10). We predict that surveys with these different telescopes will select somewhat different samples of SMBHs, with EUCLID unveiling the most massive, highest accretion rate SMBHs, Lynx the least massive, lowest accretion rate SMBHs, and JWST and ATHENA covering objects inbetween. At $z$ = 7, we predict that typical detectable SMBHs will have masses, MBH ∼ 105–8 M⊙, and Eddington normalized mass accretion rates, $\dot{M}/\dot{M}_{\mathrm{Edd}}\sim 0.6{-}2$. The SMBHs will be hosted by galaxies of stellar mass M⋆ ∼ 108–10 M⊙, and dark matter haloes of mass Mhalo ∼ 1011–12 M⊙. We predict that the detectable SMBHs at $z$ = 10 will have slightly smaller black holes, accreting at slightly higher Eddington normalized mass accretion rates, in slightly lower mass host galaxies compared to those at $z$ = 7, and reside in haloes of mass Mhalo ∼ 1010–11 M⊙.

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Black hole mass accretion rates and efficiency factors for over 750 AGN and multiple GBH

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3213 ◽

2020 ◽

Vol 500 (1) ◽

pp. 215-231

Author(s):

Ruth A Daly

Keyword(s):

Black Hole ◽

Radio Emission ◽

Binary Systems ◽

Accretion Rate ◽

Beam Power ◽

Black Hole Mass ◽

X Ray ◽

Accretion Rates ◽

Efficiency Factors ◽

The Impact

ABSTRACT Mass accretion rates in dimensionless and physical units, and efficiency factors describing the total radiant luminosity of the disc and the beam power of the outflow are obtained and studied here for samples of black hole systems with outflows. Four samples of sources including 576 LINERs, 100 classical double (FRII) radio sources, 80 relatively local AGN, and 103 measurements of four stellar mass X-ray binary systems, referred to as Galactic Black Holes (GBHs), are included in the study. All of the sources have highly collimated outflows leading to compact radio emission or powerful extended (FRII) radio emission. The properties of each of the full samples are explored, as are those of the four individual GBH, and sub-types of the FRII and local AGN samples. Source types and sub-types that have high, medium, and low values of accretion rates and efficiency factors are identified and studied. A new efficiency factor that describes the relative impact of black hole spin and mass accretion rate on the beam power is defined and studied, and is found to provide a new and interesting diagnostic. Mass accretion rates for 13 sources and efficiency factors for 6 sources are compared with values obtained independently, and indicate that similar values are obtained with independent methods. The mass accretion rates and efficiency factors obtained here substantially increase the number of values available, and improve our understanding of their relationship to source types. The redshift dependence of quantities is presented and the impact on the results is discussed.

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Giant planet formation models with a self-consistent treatment of heavy-element.

10.5194/epsc2020-648 ◽

2020 ◽

Author(s):

Claudio Valletta ◽

Ravit Helled

Keyword(s):

Internal Structure ◽

Heavy Element ◽

Accretion Rate ◽

Giant Planet ◽

Accretion Rates ◽

Formation And Evolution ◽

Element Enrichment ◽

Gas Accretion ◽

Consistent Treatment ◽

The Impact

We present a new numerical framework to model the formation and evolution of giant planets. The code is based on the further development of the stellar evolution toolkit Modules for Experiments in Stellar Astrophysics (MESA).&#160; The model includes the dissolution of the accreted planetesimals/pebbles in the planetary gaseous envelope, and the effect of envelope enrichment on the planetary growth and internal structure is computed self-consistently.&#160; We apply our simulations to Jupiter and investigate the impact of different heavy-element and gas accretion rates on its formation history.&#160; We show that the assumed runaway gas accretion rate significantly affect the planetary radius and luminosity. It is confirmed that heavy-element enrichment leads to shorter formation timescales due to more efficient gas accretion.&#160; We find that with heavy-element enrichment Jupiter's formation timescale is compatible with typical disks' lifetimes even when assuming a low heavy-element accretion rate (oligarchic regime).&#160; Finally, we provide an approximation for the heavy-element profile in the innermost part of the planet, providing a link between the internal structure and the planetary growth history.

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Spectroscopic properties of the dwarf nova-type cataclysmic variables observed by LAMOST

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa065 ◽

2020 ◽

Vol 72 (5) ◽

Author(s):

Zhongtao Han ◽

Soonthornthum Boonrucksar ◽

Shengbang Qian ◽

Fang Xiaohui ◽

Qishan Wang ◽

...

Keyword(s):

Emission Line ◽

Spectral Type ◽

Orbital Period ◽

White Dwarf ◽

Accretion Rate ◽

Cataclysmic Variables ◽

Spectroscopic Properties ◽

Accretion Disc ◽

Spectral Features ◽

Dwarf Novae

Abstract Spectra of 76 known dwarf novae from the LAMOST survey were presented. Most of the objects were observed in quiescence, and about 16 systems have typical outburst spectra. 36 of these systems were observed by SDSS, and most of their spectra are similar to the SDSS spectra. Two objects, V367 Peg and V537 Peg, are the first spectra of the object. The spectrum of V367 Peg shows a contribution from an M-type donor and its spectral type could be estimated as M3-5 by combining its orbital period. The signature of a white dwarf spectrum can be seen clearly in four low-accretion-rate WZ Sge stars. Other special spectral features worthy of further observations are also noted and discussed. We present a LAMOST spectral atlas of outbursting dwarf novae. Six objects have their first outburst spectra given here, and the others were also compared with the published outburst spectra. We argue that these data will be useful for further investigation of the accretion disc properties. The He ii λ4686 emission line can be found in the outburst spectra of seven dwarf novae. These objects are excellent candidates for probing the spiral asymmetries of accretion disc.

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The hydrogen Balmer lines and jump in absorption in accretion disc modelling – an ultraviolet–optical spectral analysis of the dwarf novae UZ Serpentis and CY Lyrae

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1093 ◽

2020 ◽

Vol 494 (4) ◽

pp. 5244-5258

Author(s):

Patrick Godon ◽

Edward M Sion ◽

Paula Szkody ◽

William P Blair

Keyword(s):

Spectral Analysis ◽

Accretion Rate ◽

Cataclysmic Variables ◽

Outer Radius ◽

Accretion Disc ◽

Absorption Lines ◽

Dwarf Novae ◽

Balmer Lines ◽

Flux Level ◽

The Continuum

ABSTRACT The spectra of disc-dominated cataclysmic variables (CVs) often deviate from the spectra of accretion disc models; in particular, the Balmer jump and absorption lines are found to be shallower in the observations than in the models. We carried out a combined ultraviolet–optical spectral analysis of two dwarf novae (DNe): UZ Ser in outburst, decline, and quiescence, and CY Lyr on the rise to outburst and in outburst. We fit the Balmer jump and absorption lines, the continuum flux level and slope by adjusting the accretion rate, inclination, and disc outer radius. For both systems, we find an accretion rate $\dot{M} \approx 8 \times 10^{-9}\,\mathrm{ M}_\odot\,\mathrm{ yr}^{-1}$ in outburst, and $\dot{M} \approx 2-3 \times 10^{-9}\,\mathrm{ M}_\odot\,\mathrm{ yr}^{-1}$ for the rise and decline phases. The outer disc radius we derive is smaller than expected (Rdisc ≈ 0.2a, where a is the binary separation), except during late rise (for CY Lyr) where Rdisc = 0.3a. UZ Ser also reveals a 60 000 K white dwarf. These results show that during a DN cycle the radius of the disc is the largest just before the peak of the outburst, in qualitative agreement with the disc instability model for DN outbursts. We suspect that an additional emitting component (e.g. disc wind) is also at work to reduce the slope of the continuum and size of the Balmer jump and absorption lines. We stress that both the outer disc radius and disc wind need to be taken into account for more realistic disc modelling of CVs.

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Polarized Emission and the Discovery of New Magnetic CVs

International Astronomical Union Colloquium ◽

10.1017/s0252921100001809 ◽

2004 ◽

Vol 190 ◽

pp. 22-32

Author(s):

Gary D. Schmidt

Keyword(s):

Gravitational Radiation ◽

Accretion Rate ◽

Cataclysmic Variables ◽

Selection Effects ◽

Optical Polarization ◽

Angular Momentum Loss ◽

Cyclotron Emission ◽

Magnetic Cataclysmic Variables ◽

Current Sample ◽

Cool White Dwarfs

AbstractRecent quasar surveys have identified several new magnetic cataclysmic variables accreting at remarkably low rates, ~10−13M⊙ yr−1. The new discoveries raise questions regarding selection effects that may influence the current sample and the traditional evolutionary conclusions that have been drawn. This paper reviews the techniques that have been used to identify polars, including a summary of the optical polarization as a function of accretion rate and magnetic field strength. The new, low-ṁ systems accrete without a shock and cooling is dominated by optical cyclotron emission in very well-defined harmonics. These binaries, which have been found to accrete at far below the rate corresponding to angular momentum loss by gravitational radiation, also appear to contain unusually cool white dwarfs, suggesting that they are either at an advanced age or in unusual evolutionary states.

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A Comparative Analysis on Probability of Volatility Clusters on Cryptocurrencies, and FOREX Currencies

Journal of Risk and Financial Management ◽

10.3390/jrfm14070308 ◽

2021 ◽

Vol 14 (7) ◽

pp. 308

Author(s):

Usha Rekha Chinthapalli

Keyword(s):

Investment Decision ◽

Theoretical Work ◽

Financial Asset ◽

Dynamic Features ◽

Asset Return ◽

Financial Variables ◽

Ann Models ◽

Hidden Layer ◽

Association Structure ◽

The Impact

In recent years, the attention of investors, practitioners and academics has grown in cryptocurrency. Initially, the cryptocurrency was designed as a viable digital currency implementation, and subsequently, numerous derivatives were produced in a range of sectors, including nonmonetary activities, financial transactions, and even capital management. The high volatility of exchange rates is one of the main features of cryptocurrencies. The article presents an interesting way to estimate the probability of cryptocurrency volatility clusters. In this regard, the paper explores exponential hybrid methodologies GARCH (or EGARCH) and through its portrayal as a financial asset, ANN models will provide analytical insight into bitcoin. Meanwhile, more scalable modelling is needed to fit financial variable characteristics such as ANN models because of the dynamic, nonlinear association structure between financial variables. For financial forecasting, BP is contained in the most popular methods of neural network training. The backpropagation method is employed to train the two models to determine which one performs the best in terms of predicting. This architecture consists of one hidden layer and one input layer with N neurons. Recent theoretical work on crypto-asset return behavior and risk management is supported by this research. In comparison with other traditional asset classes, these results give appropriate data on the behavior, allowing them to adopt the suitable investment decision. The study conclusions are based on a comparison between the dynamic features of cryptocurrencies and FOREX Currency’s traditional mass financial asset. Thus, the result illustrates how well the probability clusters show the impact on cryptocurrency and currencies. This research covers the sample period between August 2017 and August 2020, as cryptocurrency became popular around that period. The following methodology was implemented and simulated using Eviews and SPSS software. The performance evaluation of the cryptocurrencies is compared with FOREX currencies for better comparative study respectively.

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Model-Based Control of Torque and Nitrogen Oxide Emissions in a Euro VI 3.0 L Diesel Engine through Rapid Prototyping

Energies ◽

10.3390/en14041107 ◽

2021 ◽

Vol 14 (4) ◽

pp. 1107

Author(s):

Stefano d’Ambrosio ◽

Roberto Finesso ◽

Gilles Hardy ◽

Andrea Manelli ◽

Alessandro Mancarella ◽

...

Keyword(s):

Diesel Engine ◽

Rapid Prototyping ◽

Nitrogen Oxide ◽

Thermal State ◽

Pollutant Emissions ◽

Computational Time ◽

Nox Emissions ◽

Model Based ◽

Brake Mean Effective Pressure ◽

The Impact

In the present paper, a model-based controller of engine torque and engine-out Nitrogen oxide (NOx) emissions, which was previously developed and tested by means of offline simulations, has been validated on a FPT F1C 3.0 L diesel engine by means of rapid prototyping. With reference to the previous version, a new NOx model has been implemented to improve robustness in terms of NOx prediction. The experimental tests have confirmed the basic functionality of the controller in transient conditions, over different load ramps at fixed engine speeds, over which the average RMSE (Root Mean Square Error) values for the control of NOx emissions were of the order of 55–90 ppm, while the average RMSE values for the control of brake mean effective pressure (BMEP) were of the order of 0.25–0.39 bar. However, the test results also highlighted the need for further improvements, especially concerning the effect of the engine thermal state on the NOx emissions in transient operation. Moreover, several aspects, such as the check of the computational time, the impact of the controller on other pollutant emissions, or on the long-term engine operations, will have to be evaluated in future studies in view of the controller implementation on the engine control unit.

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