Abstract Galactic X-ray sources are diverse, ranging from active M dwarfs to compact object binaries, and everything in between. The X-ray landscape of today is rich, with point source catalogs such ...as those from XMM-Newton, Chandra, and Swift, each with ≳10 5 sources and growing. Furthermore, X-ray astronomy is on the verge of being transformed through data releases from the all-sky SRG/eROSITA survey. Many X-ray sources can be associated with an optical counterpart, which in the era of Gaia, can be determined to be Galactic or extragalactic through parallax and proper motion information. Here, I present a simple diagram—the “X-ray Main Sequence,” which distinguishes between compact objects and active stars based on their optical color and X-ray-to-optical flux ratio ( F X / F opt ). As a proof of concept, I present optical spectroscopy of six exotic accreting WDs discovered using the X-ray Main Sequence as applied to the XMM-Newton catalog. Looking ahead to surveys of the near future, I additionally present SDSS-V optical spectroscopy of new systems discovered using the X-ray Main Sequence as applied to the SRG/eROSITA eFEDS catalog.
Magnetic freezing is nowadays established as a commercial reality mainly oriented towards the food market. According to advertisements, magnetic freezing is able to generate tiny ice crystals ...throughout the frozen product, prevent cell destruction, and preserve the quality of fresh food intact after thawing. If all these advantages were true, magnetic freezing would represent a significant advance in freezing technology, not only for food preservation, but also for cryopreservation of biological specimens such as cells, tissues, and organs. Magnetic fields (MFs) are supposed to act directly on water by orientating, vibrating, and/or spinning molecules to prevent them from clustering and, thus, to promote supercooling. However, many doubts exist about the real effects of MFs on freezing and the science behind the potential mechanisms involved. To provide a basis for extending the understanding of magnetic freezing, this paper presents a critical review of the materials published in the literature up to now, including both patents and experimental results. After examining the information available, it was not possible to discern whether MFs have an appreciable effect on supercooling, freezing kinetics, ice crystals, quality, and/or viability of the frozen products. Experiments described in the literature frequently fail to identify and/or control all the factors that can play a role in magnetic freezing. Moreover, many of the comparisons between magnetic and conventional freezing are not correctly designed to draw valid conclusions, and wide ranges of MF intensities and frequencies are unexplored. Therefore, more rigorous experimentation and further evidence are needed to confirm or reject the efficacy of MFs in improving the quality of frozen products.
A Sun-like star orbiting a black hole El-Badry, Kareem; Rix, Hans-Walter; Quataert, Eliot ...
Monthly notices of the Royal Astronomical Society,
01/2023, Letnik:
518, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
We report discovery of a bright, nearby ($G = 13.8;\, \, d = 480\, \rm pc$) Sun-like star orbiting a dark object. We identified the system as a black hole candidate via its astrometric ...orbital solution from the Gaia mission. Radial velocities validated and refined the Gaia solution, and spectroscopy ruled out significant light contributions from another star. Joint modelling of radial velocities and astrometry constrains the companion mass of $M_2 = 9.62\pm 0.18\, \mathrm{M}_{\odot }$. The spectroscopic orbit alone sets a minimum companion mass of $M_2\gt 5\, \mathrm{M}_{\odot }$; if the companion were a $5\, \mathrm{M}_{\odot }$ star, it would be 500 times more luminous than the entire system. These constraints are insensitive to the mass of the luminous star, which appears as a slowly rotating G dwarf ($T_{\rm eff}=5850\, \rm K$, log g = 4.5, $M=0.93\, \mathrm{M}_{\odot }$), with near-solar metallicity ($\rm Fe/H = -0.2$) and an unremarkable abundance pattern. We find no plausible astrophysical scenario that can explain the orbit and does not involve a black hole. The orbital period, Porb = 185.6 d, is longer than that of any known stellar-mass black hole binary. The system’s modest eccentricity (e = 0.45), high metallicity, and thin-disc Galactic orbit suggest that it was born in the Milky Way disc with at most a weak natal kick. How the system formed is uncertain. Common envelope evolution can only produce the system’s wide orbit under extreme and likely unphysical assumptions. Formation models involving triples or dynamical assembly in an open cluster may be more promising. This is the nearest known black hole by a factor of 3, and its discovery suggests the existence of a sizable population of dormant black holes in binaries. Future Gaia releases will likely facilitate the discovery of dozens more.
Abstract
We apply a conventional accretion disk model to the FU Ori–type objects HBC 722 and Gaia 17bpi. Our base model is a steady-state, thin Keplerian disk featuring a modified Shakura–Sunyaev ...temperature profile, with each annulus radiating as an area-weighted spectrum given by a NextGen atmosphere at the appropriate temperature. We explore departures from the standard model by altering the temperature distribution in the innermost region of the disk to account for “boundary region”–like effects. We consider the overall spectral energy distribution as well as medium- and high-resolution spectra in evaluating best-fit models to the data. Parameter degeneracies are studied via a Markov Chain Monte Carlo parameter estimation technique. Allowing all parameters to vary, we find accretion rates for HBC 722 of
M
̇
=
10
−
4.90
M
⊙
yr
−
1
−
0.40
+
0.99
dex
and for Gaia 17bpi of
M
̇
=
10
−
6.70
M
⊙
yr
−
1
−
0.36
+
0.46
dex
;
the corresponding maximum disk temperatures are
7100
−
500
+
300
K and
7900
−
400
+
900
K, respectively. While the accretion rate of HBC 722 is on the same order as other FU Ori–type objects, Gaia 17bpi has a lower rate than previously reported as typical, commensurate with its lower luminosity. Alternate models that fix some disk or stellar parameters are also presented, with tighter confidence intervals on the remaining fitted parameters. In order to improve upon the somewhat large credible intervals for the
M
̇
values, and to make progress on boundary layer characterization, flux-calibrated ultraviolet spectroscopy is needed.
Since the early 2000s, electromagnetic freezers have been sold all over the world. According to the manufacturers, the oscillating magnetic fields (OMFs) applied by these devices are capable of ...avoiding ice damage in frozen foods. To assess the effectiveness of OMFs in preserving food quality, we froze crab sticks in a commercial electromagnetic freezer, both with (<2 mT, 6–59 Hz) and without OMF application. Crab sticks were also frozen in a conventional freezer, both with static- and forced-air conditions, to compare electromagnetic freezing with conventional methods. After 24 h and 1, 3, 6, 9, and 12 months of storage, we did not find any effect of the OMFs on the drip loss, water-holding capacity, toughness, and whiteness of the crab sticks frozen in the electromagnetic device. Moreover, no advantage of electromagnetic freezing over air-blast freezing was detected at the conditions tested. More experiments at larger magnetic field strength and wider frequency ranges are needed to have a complete view of the potential effects of OMFs on food freezing.
•Crab sticks were frozen in both an electromagnetic and a conventional freezer.•Several quality attributes were assessed after 0–12 months of frozen storage.•Electromagnetic freezing failed to retain the quality of fresh crab sticks unaltered.•Oscillating magnetic fields produced no effect on the quality of the frozen samples.•No advantage of electromagnetic freezing over air-blast freezing was observed.
A red giant orbiting a black hole El-Badry, Kareem; Rix, Hans-Walter; Cendes, Yvette ...
Monthly notices of the Royal Astronomical Society,
03/2023, Letnik:
521, Številka:
3
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
We report spectroscopic and photometric follow-up of a dormant black hole (BH) candidate from Gaia DR3. The system, which we call Gaia BH2, contains a ∼1 M⊙ red giant and a dark companion ...with mass $M_2 = 8.9\pm 0.3\, {\rm M}_{\odot }$ that is very likely a BH. The orbital period, Porb = 1277 d, is much longer than that of any previously studied BH binary. Our radial velocity (RV) follow-up over a 7-month period spans >90 per cent of the orbit’s RV range and is in excellent agreement with the Gaia solution. UV imaging and high-resolution optical spectra rule out plausible luminous companions that could explain the orbit. The star is a bright (G = 12.3), slightly metal-poor ($\rm Fe/H=-0.22$) low-luminosity giant ($T_{\rm eff}=4600\, \rm K$; $R = 7.8\, R_{\odot }$; $\log \leftg/\left({\rm cm\, s^{-2}}\right)\right = 2.6$). The binary’s orbit is moderately eccentric (e = 0.52). The giant is enhanced in α-elements, with $\rm \alpha /Fe = +0.26$, but the system’s Galactocentric orbit is typical of the thin disc. We obtained X-ray and radio non-detections of the source near periastron, which support BH accretion models in which the net accretion rate at the horizon is much lower than the Bondi–Hoyle–Lyttleton rate. At a distance of 1.16 kpc, Gaia BH2 is the second-nearest known BH, after Gaia BH1. Its orbit – like that of Gaia BH1 – seems too wide to have formed through common envelope evolution. Gaia BH1 and BH2 have orbital periods at opposite edges of the Gaia DR3 sensitivity curve, perhaps hinting at a bimodal intrinsic period distribution for wide BH binaries. Dormant BH binaries like Gaia BH1 and Gaia BH2 significantly outnumber their close, X-ray bright cousins, but their formation pathways remain uncertain.
Previous papers in the literature show no agreement on the effects of static magnetic fields (SMFs) on water supercooling and freezing kinetics. Hypothetical effects of the SMF orientation and the ...presence of ions in the sample are also unclear. To shed light on this matter, we froze 10-mL pure water samples and 0.9% NaCl solutions subjected or not to the SMFs generated by two magnets. We found that the relative position of the magnet poles affected the magnetic field orientation, strength, and the spatial magnetic gradients established throughout the sample. Thus, the SMF strength ranged from 107 to 359 mT when unlike magnet poles faced each other whereas it ranged from 0 to 241 mT when like magnet poles were next to each other. At both conditions, we did not detect any effect of the SMFs on the time at which nucleation occurred, the extent of supercooling, and the phase transition and total freezing times in both pure water and 0.9% NaCl solutions. More experiments, under well-characterized SMFs, should be performed to definitively evaluate the ability of SMFs in improving food freezing.
•The relative position of the magnet poles affected the SMF orientation and strength.•Significant spatial magnetic gradients were established throughout the samples.•Magnetic gradients were in the 107–359 mT and 0–241 mT range in SMF-A and SMF-R samples.•SMFs produced no effect on supercooling and freezing kinetics of water and 0.9% NaCl solutions.•An accurate SMF characterization is needed to assess the effect of SMFs on freezing.
Describe the histological findings of minimally ultrasound-guided invasive autopsies in deceased patients with severe SARS-CoV-2 and compare the diagnostic yield with open autopsies.
Observational ...post-mortem cohort study. Minimally invasive ultrasound-guided autopsies were performed in fourteen deceased patients with a confirmed diagnosis of SARS-CoV-2 pneumonia. Histological and clinical findings of lung, kidney, and liver tissue are described and contrasted with those previously reported in the literature.
Single-center COVID-19 reference center in Mexico City.
Fourteen minimally invasive autopsies revealed a gross correlation with open autopsies reports: 1) Lung histology was characterized mainly by early diffuse alveolar damage (12/13). Despite low lung compliances and prolonged mechanical ventilation, the fibrotic phase was rarely observed (2/13). 2) Kidney histopathology demonstrated acute tubular injury (12/13), interstitial nephritis (11/13), and glomerulitis (11/13) as the predominant features 3) Liver histology was characterized by neutrophilic inflammation in all of the cases, as well as hepatic necrosis (8/14) despite minimal alterations in liver function testing. Hepatic steatosis was observed in most cases (12/14). SARS-CoV-2 positivity was widely observed throughout the immunohistochemical analysis. However, endothelitis and micro thrombosis, two of the hallmark features of the disease, were not observed.
Our data represents the largest minimally invasive, ultrasound-guided autopsy report. We demonstrate a gross histological correlation with large open autopsy cohorts. However, this approach might overlook major histologic features of the disease, such as endothelitis and micro-thrombosis. Whether this represents sampling bias is unclear.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
ABSTRACT
We constrain the orbital period (Porb) distribution of low-mass detached main-sequence eclipsing binaries (EBs) with light-curves from the Zwicky Transient Facility (ZTF), which provides a ...well-understood selection function and sensitivity to faint stars. At short periods (Porb ≲ 2 d), binaries are predicted to evolve significantly due to magnetic braking (MB), which shrinks orbits and ultimately brings detached binaries into contact. The period distribution is thus a sensitive probe of MB. We find that the intrinsic period distribution of low-mass (0.1 ≲ M1/M⊙ < 0.9) binaries is basically flat (${\rm d}N/{\rm d}P_{\rm orb} \propto P_{\rm orb}^0$) from Porb = 10 d down to the contact limit. This is strongly inconsistent with predictions of classical MB models based on the Skumanich relation, which are widely used in binary evolution calculations and predict ${\rm d}N/{\rm d}P_{\rm orb} \propto P_{\rm orb}^{7/3}$ at short periods. The observed distributions are best reproduced by models in which the magnetic field saturates at short periods with a MB torque that scales roughly as $\dot{J}\propto P_{\rm orb}^{-1}$, as opposed to $\dot{J} \propto P_{\rm orb}^{-3}$ in the standard Skumanich law. We also find no significant difference between the period distributions of binaries containing fully and partially convective stars. Our results confirm that a saturated MB law, which was previously found to describe the spin-down of rapidly rotating isolated M dwarfs, also operates in tidally locked binaries. We advocate using saturated MB models in binary evolution calculations. Our work supports previous suggestions that MB in cataclysmic variables (CVs) is much weaker than assumed in the standard evolutionary model, unless mass transfer leads to significant additional angular momentum loss in CVs.
ABSTRACT
We present multi-epoch spectroscopic follow-up of a sample of ellipsoidal variables selected from Gaia Data Release 3 (DR3) as candidates for hosting quiescent black holes (BHs) and neutron ...stars (NSs). Our targets were identified as BH/NS candidates because their optical light curves – when interpreted with models that attribute variability to tidal distortion of a star by a companion that contributes negligible light – suggest that the companions are compact objects. From the likely BH/NS candidates identified in recent work accompanying Gaia DR3, we select 14 of the most promising targets for follow-up. We obtained spectra for each object at 2–10 epochs, strategically observing near conjunction to best constrain the radial velocity semi-amplitude. From the measured semi-amplitudes of the radial velocity curves, we derive minimum companion masses of $M_{2,\, \rm min} \le 0.5 \, {\rm M}_{\odot }$ in all cases. Assuming random inclinations, the typical inferred companion mass is $M_2 \sim 0.15\, {\rm M}_{\odot }$. This makes it unlikely that any of these systems contain a BH or NS, and we consider alternative explanations for the observed variability. We can best reproduce the observed light curves and radial velocities with models for unequal-mass contact binaries with star-spots. Some of the objects in our sample may also be detached main-sequence binaries, or even single stars with pulsations or star-spot variability masquerading as ellipsoidal variation. We provide recommendations for future spectroscopic efforts to further characterize this sample and more generally to search for compact object companions in close binaries.
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