We present the first volume-limited sample of spectroscopically confirmed hot subluminous stars out to 500 pc, defined using the accurate parallax measurements from the Gaia space mission data ...release 3 (DR3). The sample comprises a total of 397 members, with 305 (~77%) identified as hot subdwarf stars, including 83 newly discovered systems. Of these, we observe that 178 (~58%) are hydrogen-rich sdBs, 65 are sdOBs (~21%), 32 are sdOs (~11%), and 30 are He-sdO/Bs (~10%). Among them, 48 (~16%) exhibit an infrared excess in their spectral energy distribution fits, suggesting a composite binary system. The hot subdwarf population is estimated to be 90% complete, assuming that most missing systems are these composite binaries located within the main sequence (MS) in the Gaia colour-magnitude diagram. The remaining sources in the sample include cataclysmic variables, blue horizontal branch stars, hot white dwarfs, and MS stars. We derived the mid-plane density ρ 0 and scale height h z for the non-composite hot subdwarf star population using a hyperbolic sechant profile (sech 2 ). The best-fit values are ρ 0 = 5.17 ± 0.33 × 10 −7 stars pc −3 and h z = 281 ± 62 pc. When accounting for the composite-colour hot subdwarfs and their estimated completeness, the mid-plane density increases to ρ 0 = 6.15 −0.53 +1.16 × 10 −7 stars pc −3 . This corrected space density is an order of magnitude lower than predicted by population synthesis studies, supporting previous observational estimates.
2M1938+4603 (KIC 9472174) displays a spectacular light curve dominated by a strong reflection effect and rather shallow, grazing eclipses. The orbital period is 0.126 d, the second longest period yet ...found for an eclipsing sdB+dM, but still close to the minimum 0.1-d period among such systems. The phase-folded Kepler light curve was used to detrend the orbital effects from the data set. The amplitude spectrum of the residual light curve reveals a rich collection of pulsation peaks spanning frequencies from ∼50 to 4500 μHz. The presence of a complex pulsation spectrum in both the p- and g-mode regions has never before been reported in a compact pulsator. Eclipsing sdB+dM stars are very rare, with only seven systems known and only one with a pulsating primary. Pulsating stars in eclipsing binaries are especially important since they permit masses derived from seismological model fits to be cross-checked with orbital mass constraints. We present a first analysis of this star based on the Kepler 9.7-d commissioning light curve and extensive ground-based photometry and spectroscopy that allow us to set useful bounds on the system parameters. We derive a radial-velocity amplitude K1 = 65.7 ± 0.6 km s −1, inclination angle , and find that the masses of the components are M1 = 0.48 ± 0.03 M⊙ and M2 = 0.12 ± 0.01 M⊙.
ABSTRACT
We report the discovery of two hot Jupiters orbiting the stars K2-237 and K2-238. We used photometric data from Campaigns 11 and 12 of the Kepler K2 mission and radial velocity data obtained ...using the HARPS, FEROS, and CORALIE spectrographs. K2-237 b and K2-238 b have masses of $1.60^{+0.11}_{-0.11}$ and $0.86^{+0.13}_{-0.12}\,M_\mathrm{Jup}$, radii of $1.65^{+0.07}_{-0.08}$ and $1.30^{+0.15}_{-0.14}\,R_\mathrm{Jup}$, and are orbiting their host stars in 2.18- and 3.20-d orbits, respectively. The large radius of K2-237 b leads us to conclude that this candidate corresponds to a highly inflated hot Jupiter. K2-238 b has a radius consistent with theoretical models, considering the high incident flux falling on the planet. We consider K2-237 b to be an excellent system for follow-up studies, since not only is it very inflated, but it also orbits a relatively bright star (V = 11.6).
Asteroseismology offers the possibility of probing stellar interiors and testing evolutionary and seismic models. Precise photometry and spectroscopy obtained during multi-site campaigns on young ...open clusters allows discovering rich samples of pulsating stars and using them in a simultaneous seismic modelling called ensemble asteroseismology. The aim of this study is to obtain the age of the open cluster NGC 6910 by means of ensemble asteroseismology of the early-type pulsating members, to derive their stellar parameters, and to classify the excited modes. We used time-series analysis, performed photometric and spectroscopic mode identification, and calculated grids of evolutionary and seismic models to apply the procedure of ensemble asteroseismology for nine pulsating members of NGC 6910. With two iterations of the procedure of ensemble asteroseismology applied to nine pulsating stars we derived an age of 10.6 −0.8+0.9 − 0.8 + 0.9 $ ^{+0.9}_{-0.8} $ Myr for NGC 6910. We also identified the degree l for 8 of 37 modes detected in these stars and classified all modes in terms of p, g, and mixed-mode pulsations. Of the nine pulsating stars examined in the paper, eight are β Cep stars, including three that are hybrid β Cep and slowly pulsating B-type (SPB) pulsators, and one is an SPB star. Interestingly, the least massive β Cep star, NGC 6910-38, has a mass of about 5.6 M⊙. The present theory does not predict unstable p modes in B-type stars with such a low mass. The g modes with relatively high frequencies (> 3.5 d−1), observed in three members of the cluster, are also stable according to seismic modelling. Both findings pose a challenge for theoretical calculations and prompt a revision of the opacities. The procedure of ensemble asteroseismology was found to be successful for NGC 6910 and χ Per on the basis of pulsating B-type stars and can therefore be applied to other young open clusters that are rich in such stars.
Researchers have employed various methods to identify symptom clusters in cardiovascular conditions, without identifying rationale. Here, we test clustering techniques and outcomes using a data set ...from patients with acute coronary syndrome. A total of 474 patients who presented to emergency departments in five United States regions were enrolled. Symptoms were assessed within 15 min of presentation using the validated 13-item ACS Symptom Checklist. Three variable-centered approaches resulted in four-factor solutions. Two of three person-centered approaches resulted in three-cluster solutions. K-means cluster analysis revealed a six-cluster solution but was reduced to three clusters following cluster plot analysis. The number of symptoms and patient characteristics varied within clusters. Based on our findings, we recommend using (a) a variable-centered approach if the research is exploratory, (b) a confirmatory factor analysis if there is a hypothesis about symptom clusters, and (c) a person-centered approach if the aim is to cluster symptoms by individual groups.
TESS first look at evolved compact pulsators Charpinet, S.; Brassard, P.; Fontaine, G. ...
Astronomy and astrophysics (Berlin),
12/2019, Letnik:
632
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
The TESS satellite was launched in 2018 to perform high-precision photometry from space over almost the whole sky in a search for exoplanets orbiting bright stars. This instrument has opened ...new opportunities to study variable hot subdwarfs, white dwarfs, and related compact objects. Targets of interest include white dwarf and hot subdwarf pulsators, both carrying high potential for asteroseismology.
Aims.
We present the discovery and detailed asteroseismic analysis of a new
g
-mode hot B subdwarf (sdB) pulsator, EC 21494−7018 (TIC 278659026), monitored in TESS first sector using 120-s cadence.
Methods.
The TESS light curve was analyzed with standard prewhitening techniques, followed by forward modeling using our latest generation of sdB models developed for asteroseismic investigations. By simultaneously best-matching all the observed frequencies with those computed from models, we identified the pulsation modes detected and, more importantly, we determined the global parameters and structural configuration of the star.
Results.
The light curve analysis reveals that EC 21494−7018 is a sdB pulsator counting up to 20 frequencies associated with independent
g
-modes. The seismic analysis singles out an optimal model solution in full agreement with independent measurements provided by spectroscopy (atmospheric parameters derived from model atmospheres) and astrometry (distance evaluated from
Gaia
DR2 trigonometric parallax). Several key parameters of the star are derived. Its mass (0.391 ± 0.009
M
⊙
) is significantly lower than the typical mass of sdB stars and suggests that its progenitor has not undergone the He-core flash; therefore this progenitor could originate from a massive (≳2
M
⊙
) red giant, which is an alternative channel for the formation of sdBs. Other derived parameters include the H-rich envelope mass (0.0037 ± 0.0010
M
⊙
), radius (0.1694 ± 0.0081
R
⊙
), and luminosity (8.2 ± 1.1
L
⊙
). The optimal model fit has a double-layered He+H composition profile, which we interpret as an incomplete but ongoing process of gravitational settling of helium at the bottom of a thick H-rich envelope. Moreover, the derived properties of the core indicate that EC 21494−7018 has burnt ∼43% (in mass) of its central helium and possesses a relatively large mixed core (
M
core
= 0.198 ± 0.010
M
⊙
), in line with trends already uncovered from other g-mode sdB pulsators analyzed with asteroseismology. Finally, we obtain for the first time an estimate of the amount of oxygen (in mass;
X
(O)
core
= 0.16
+0.13
−0.05
) produced at this stage of evolution by an helium-burning core. This result, along with the core-size estimate, is an interesting constraint that may help to narrow down the still uncertain
12
C(
α
,
γ
)
16
O nuclear reaction rate.
KPD1930+2752 is a short-period pulsating subdwarf B (sdB) star. It is also an ellipsoidal variable with a known binary period of 2.3 h. The companion is most likely a white dwarf and the total mass ...of the system is close to the Chandresekhar limit. In this paper, we report the results of Whole Earth Telescope (WET) photometric observations during 2003 and a smaller multisite campaign of 2002. From 355h of WET data, we detect 68 pulsation frequencies and suggest an additional 13 frequencies within a crowded and complex temporal spectrum between 3065 and 6343 mu Hz (periods between 326 and 157s). We examine pulsation properties including phase and amplitude stability in an attempt to understand the nature of the pulsation mechanism. We examine a stochastic mechanism by comparing amplitude variations with simulated stochastic data. We also use the binary nature of KPD1930+2752 for identifying pulsation modes via multiplet structure and a tidally induced pulsation geometry. Our results indicate a complicated pulsation structure that includes short-period ( approximately 16h) amplitude variability, rotationally split modes, tidally induced modes and some pulsations which are geometrically limited on the sdB star.
The effects of irradiation on the secondary stars of close binary systems are crucial for reliably determining the system parameters and for understanding the close binary evolution. They affect the ...stellar structure of the irradiated star and are reflected in the appearance of characteristic features in the spectroscopic and photometric data of these systems. We aim to study the light that originates from the irradiated side of the low-mass component of a close binary eclipsing system, which comprises a hot subdwarf primary and a low mass companion, to precisely interpret their high precision photometric and spectroscopic data, and accurately determine their system and surface parameters. We reanalyse the archival high-resolution time-resolved VLT/UVES spectra of AA Dor system, where irradiation features have already been detected. After removing the predominant contribution of the hot subdwarf primary, the residual spectra reveal more than 100 emission lines from the heated side of the secondary, which show maximum intensity close to the phases around the secondary eclipse. We analyse the residual spectrum to model the irradiation of the low-mass secondary. We perform a detailed analysis of 22 narrow emission lines of the irradiated secondary, mainly of O ii, with a few significant C ii lines. Their phase profiles constrain the emission region of the heated side to a radius ≥95% of the radius of the secondary, while the shape of their velocity profiles reveals two distinct asymmetry features, one at the quadrature and the other at the secondary eclipse. In addition, we identify weaker emission signatures originating from more than 70 lines, including lines from He i, N ii, Si iii, Ca ii, and Mg ii. From the emission lines of the heated side of the secondary star, we determine the radial velocity semi-amplitude of the centre-of-light and correct it to the centre-of-mass of the secondary which, in turn, gives accurate masses of both components of the AA Dor system. The resulting masses M1 = 0.46 ± 0.01 M⊙ and M2 = 0.079 ± 0.002 M⊙ are in perfect accordance with those of a canonical hot subdwarf primary and a low mass that is just at the substellar limit for the companion. We also compute a first generation atmosphere model of the low mass secondary, which includes irradiation effects and matches the observed spectrum well. We find an indication of an extended atmosphere of the irradiated secondary star.
Studies have identified sex differences in symptoms of acute coronary syndrome (ACS); however, retrospective designs, abstraction of symptoms from medical records, and variations in assessment forms ...make it difficult to determine the clinical significance of sex differences.
The aim of this study is to determine the influence of sex on the occurrence and distress of 13 symptoms for patients presenting to the emergency department for symptoms suggestive of ACS.
A total of 1064 patients admitted to 5 emergency departments with symptoms triggering a cardiac evaluation were enrolled. Demographic and clinical variables, symptoms, comorbid conditions, and functional status were measured.
The sample was predominantly male (n = 664, 62.4%), white (n = 739, 69.5%), and married (n = 497, 46.9%). Women were significantly older than men (61.3 ± 14.6 vs 59.5 ± 13.6 years). Most patients were discharged with a non-ACS diagnosis (n = 590, 55.5%). Women with ACS were less likely to report chest pain as their chief complaint and to report more nausea (odds ratio OR, 1.56; confidence interval CI, 1.00-2.42), shoulder pain (OR, 1.76; CI, 1.13-2.73), and upper back pain (OR, 2.92; CI, 1.81-4.70). Women with ACS experienced more symptoms (6.1 vs 5.5; P = .026) compared with men. Men without ACS had less symptom distress compared with women.
Women and men evaluated for ACS reported similar rates of chest pain but differed on other classic symptoms. These findings suggest that women and men should be counseled that ACS is not always accompanied by chest pain and multiple symptoms may occur simultaneously.
The 6-minute walk test is a measure of functional capacity in patients with heart failure (HF) or chronic kidney disease (CKD). The association between estimated glomerular filtration rate (eGFR) and ...6-minute walk distance (6MWD) has not been investigated in African-Americans (AA), despite them having a higher incidence of CKD and chronic HF. Thus, our aim was to determine if eGFR was an independent predictor of 6MWD in AA >50 years of age with HF.
In this cross-sectional study, we examined the relationship between eGFR and 6MWD in 45 AA patients with HF from an urban outpatient HF clinic, using logistic regression with bootstrapping.
The sample consisted of 53% females; mean age = 64.8 ± 9 years, mean eGFR = 61.6 ± 20 mL/min/1.73 m
, and mean 6MWD = 222 ± 78 m. A decrease in eGFR by 10 mL/min/1.73 m
was associated with 46% higher odds (
= 0.02) of a 6MWD ≤200 m in an unadjusted model and 39-41% higher odds (
= 0.03) of a 6MWD ≤200 m in adjusted models.
A decrease in eGFR significantly predicted a shorter 6MWD in AA patients with HF. Therefore, a reduction in eGFR may be used as an early marker to identify and manage declining functional capacity in these patients.
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