Abstracts of Interest
Selected by:
Rami Alsulami
Abstract: 2401.01468
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Title:Measuring the Stellar and Planetary Properties of the 51 Eridani System
Download PDF HTML (experimental)Abstract:In order to study exoplanets, a comprehensive characterization of the fundamental properties of the host stars, such as angular diameter, temperature, luminosity, and age, is essential, as the formation and evolution of exoplanets are directly influenced by the host stars at various points in time. In this paper, we present interferometric observations taken of directly imaged planet host 51 Eridani at the CHARA Array. We measure the limb-darkened angular diameter of HD 29391 to be $\theta_{\rm LD} = 0.450\pm 0.004 \rm ~mas$ and combining with the Gaia zero-point corrected parallax, we get a stellar radius of $1.45 \pm 0.01 \rm~R_{\odot}$. We use the PARSEC isochrones to estimate an age of $23.2^{+1.7}_{-1.6} \rm ~Myr$ and a mass of $1.550 \pm 0.005 \rm ~M_{\odot}$. The age and mass agree well with values in the literature, determined through a variety of methods ranging from dynamical age trace-backs to lithium depletion boundary methods. We derive a mass of $4.1^{+0.5}_{-0.4} \rm ~M_{Jup}$ for 51 Eri b using the Sonora Bobcat models, which further supports the possibility of 51 Eri b forming under either the hot-start formation model or the warm-start formation model.
Abstract: 2401.01122
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Title:Temperature-reducing shocks in optically-thin radiative MHD -- analytical and numerical results
Download PDF HTML (experimental)Abstract:Shocks are often invoked as heating mechanisms in astrophysical systems, with both adiabatic compression and dissipative heating that leading to temperature increases. Whilst shocks are reasonably well understood for ideal magnetohydrodynamic (MHD) systems, in many astrophysical plasmas, radiation is an important phenomena, which can allow energy to leave the system. As such, energy becomes non-conservative which can fundamentally change the behaviour of shocks. The energy emitted through optically-thin radiation post-shock can exceed the thermal energy increase, resulting in shocks that reduce the temperature of the medium, i.e., cooling shocks that have a net decrease in temperature across the interface. In this paper, semi-analytical solutions for radiative shocks are derived to demonstrate that both cooling (temperature decreasing) and heating (temperature increasing) shock solutions are possible in radiative MHD. Numerical simulations of magnetic reconnection with optically-thin radiative losses also yield both heating and cooling shocks in roughly equal abundances. The detected cooling shocks feature a significantly lower pressure jump across the shock than their heating counterparts. The compression at the shock front leads to locally-enhanced radiative losses, resulting in significant cooling within a few grid cells in the upstream and downstream directions. The presence of temperature-reducing (cooling) shocks is critical in determining the thermal evolution, and heating or cooling, across a wealth of radiative astrophysical plasmas.
Abstract: 2401.01116
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Title:Extinction, the elephant in the room that hinders optical Galactic observations
Download PDF HTML (experimental)Abstract:Extinction is the elephant in the room that almost everyone tries to avoid when analyzing optical/IR data: astronomers tend to find a quick fix for it that the referee will accept, but that does not mean such a solution is correct or even optimal. In this contribution I address three important issues related to extinction that are commonly ignored and present current and future solutions for them: [1] Extinction produces non-linear photometric effects, [2] the extinction law changes between sightlines, and [3] not all families of extinction laws have the same accuracy.
Abstract: 2401.01707
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Title:Explaining supernova remnant G352.7-0.1 as a peculiar type Ia supernova inside a planetary nebula
Download PDF HTML (experimental)Abstract:I identify a point-symmetric morphology of the supernova remnant (SNR) G352.7-0.1 and propose that the outer axially-symmetric structure is the remnant of a common envelope evolution (CEE) of the progenitor system, while the inner structure is the ejecta of a thermonuclear explosion triggered by the merger of a white dwarf (WD) and the core of an asymptotic giant branch (AGB) star. The main radio structure of SNR G352.7-0.1 forms an outer (large) ellipse. The bright X-ray emitting gas forms a smaller ellipse with a symmetry axis inclined to the symmetry axis of the large radio ellipse. The high abundance of iron and the energy of its X-ray lines suggest a type Ia supernova (SN Ia). The massive swept-up gas suggests a relatively massive progenitor system. I propose a scenario with progenitors of initial masses of M1=5-7Mo and M2=4-5 Mo. At a later phase, the WD remnant of the primary star and the AGB secondary star experience a CEE that ejects the circumstellar material that swept up more ISM to form the large elliptical radio structure. An explosion during the merger of the WD with the core of the AGB star triggered a super-Chandrasekhar thermonuclear explosion that formed the inner structure that is bright in X-ray. A tertiary star in the system caused the misalignment of the two symmetry axes. This study adds to the rich variety of evolutionary routes within the different scenarios of normal and peculiar SNe Ia.
Abstract: 2401.00923
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Title:Stacking the spectra of eROSITA galaxy cluster data for searches of the 3.5keV line: Dark matter decay or charge exchange?
No PDF available, click to view other formatsAbstract:In this Master Thesis, we use a technique to shift and stack the X-Ray spectra of 1138 galaxy clusters from the eRASS-1 survey, totalling 430649 counts. In comparison with previous stacking techniques, the method presented here introduces proper normalization of the shifted redistribution matrix file (RMF), which allows to recover the physical temperature and metallicity of the stacked spectra. Using this technique, we can obtain constraints in the stacked spectra for the individual abundances of O, Ne, Mg, Si, Ar, Ca, and Fe. Additionally, we study the possible detection of the previously reported 3.5keV unidentified line emission; however, the residuals barely exceed $\pm 2 \sigma$ in the [3-4]keV range. On the other hand, although residuals in the [3.4-3.55]keV band are compatible with charge exchange emission from SXVI (bare sulphur ions), charge exchange emission from OVII at 0.56keV should also be present, since it is 200 orders of magnitude higher than charge emission from SXVI in the [3.4-3.55]keV band; however, it is unfortunately not detected.
Abstract: 2401.02612
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Title:Measuring the Virial Factor in SDSS DR7 AGNs with Redshifted H$β$ and H$α$ Broad Emission Lines
Download PDF HTML (experimental)Abstract:Under the hypothesis of gravitational redshift induced by the central supermassive black hole, and based on line widths and shifts of redward shifted H$\beta$ and H$\alpha$ broad emission lines for more than 8000 SDSS DR7 AGNs, we measure the virial factor in determining supermassive black hole masses. The virial factor had been believed to be independent of accretion radiation pressure on gas clouds in broad-line region (BLR), and only dependent on inclination effects of BLR. The virial factor measured spans a very large range. For the vast majority of AGNs ($>$96%) in our samples, the virial factor is larger than $f=1$ usually used in literatures. The $f$ correction makes the percent of high-accreting AGNs decrease by about 100 times. There are positive correlations of $f$ with the dimensionless accretion rate and Eddington ratio. The redward shifts of H$\beta$ and H$\alpha$ are mainly the gravitational origin, confirmed by a negative correlation between the redward shift and the dimensionless radius of BLR. Our results show that radiation pressure force is a significant contributor to the measured virial factor, containing the inclination effects of BLR. The usually used values of $f$ should be corrected for high-accreting AGNs, especially high redshift quasars. The $f$ correction increases their masses by one--two orders of magnitude, which will make it more challenging to explain the formation and growth of supermassive black holes at high redshifts.
Abstract: 2401.02519
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Title:Ages and metallicities of globular clusters in M81 using GTC/OSIRIS spectra
Download PDF HTML (experimental)Abstract:We here present the results of an analysis of the optical spectroscopy of 42 globular cluster (GC) candidates in the nearby spiral galaxy M81 (3.61~Mpc). The spectra were obtained using the long-slit and MOS modes of the OSIRIS instrument at the 10.4~m Gran Telescopio Canarias (GTC) at a spectral resolution of $\sim$1000. We used the classical H$\beta$ vs [MgFe]$'$ index diagram to separate genuine old GCs from clusters younger than 3 Gyr. Of the 30 spectra with continuum signal-to-noise ratio $>10$, we confirm 17 objects to be classical GCs (age $>10$~Gyr, $-1.4<$[Fe/H]$<-$0.4), with the remaining 13 being intermediate-age clusters (1-7.5~Gyr). We combined age and metallicity data of other nearby spiral galaxies ($\lesssim18$~Mpc) obtained using similar methodology like the one we have used here to understand the origin of GCs in spiral galaxies in the cosmological context. We find that the metal-poor ([Fe/H]<$-$1) GCs continued to form up to 6~Gyr after the first GCs were formed, with all younger systems (age $<8$~Gyr) being metal-rich.
This page created: Mon Jan 22 14:09:54 ACDT 2024 by Rami Alsulami
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