HD 105 is a nearby, pre-main-sequence G0 star hosting a moderately bright debris disk (Ldust/L ∼ 2.6 × 10−4). The star and its surroundings might therefore be considered an analog of the young solar ...system. We refine the stellar parameters based on an improved Gaia parallax distance and identify it as a pre-main-sequence star with an age of 50 16 Myr. The circumstellar disk was marginally resolved by Herschel/PACS imaging at far-infrared wavelengths. Here, we present an archival ALMA observation at 1.3 mm, revealing the extent and orientation of the disk. We also present Hubble Space Telescope (HST)/NICMOS and VLT/SPHERE near-infrared images, where we recover the disk in scattered light at the ≥5 level. This was achieved by employing a novel annular averaging technique and is the first time this has been achieved for a disk in scattered light. Simultaneous modeling of the available photometry, disk architecture, and detection in scattered light allow better determination of the disk's architecture, and dust grain minimum size, composition, and albedo. We measure the dust albedo to lie between 0.19 and 0.06, the lower value being consistent with Edgeworth-Kuiper Belt objects.
Abstract We propose and discuss a new experimental approach to measure the centroid shift induced by gravitational microlensing in the images of lensed quasars (astrometric microlensing). Our ...strategy is based on taking the photocenter of a region in the quasar large enough as to be insensitive to microlensing as reference to measure the centroid displacement of the continuum. In this way, single-epoch measurements of astrometric microlensing can be performed. Using numerical simulations, we show that, indeed, the centroid shift monotonically decreases as the size of the emitting region increases, and only for relatively large regions, like the broad line region (BLR), does the centroid shift become negligible. This opens interesting possibilities to study the stratification of the different emitters in the accretion disk and the BLR. We estimate the amplitude of the centroid shifts for 79 gravitationally lensed images and study more thoroughly the special cases Q2237+030 A, RXJ1131-1231 A, PG1115+080 A2, and SDSS J1004+4112 A. We propose to use spectro-astrometry to simultaneously obtain the photocenters of the continuum and of different emission line regions since, with the precision of forthcoming instruments, astrometric microlensing by ∼1 M ⊙ mass microlenses may be detected in many quasar lensed images. When we consider more massive micro/millilenses, M ≳ 10 M ⊙ , often proposed as the constituents of dark matter, the BLR becomes sensitive to microlensing and can no longer be used as a positional reference to measure centroid shifts. Differential microlensing between the images of a lensed quasar along several epochs should be used instead.
Context. Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their solar system counterparts are the asteroid and Edgeworth-Kuiper ...belts. Aims. The DUNES survey aims at detecting extra-solar analogues to the Edgeworth-Kuiper belt around solar-type stars, putting in this way the solar system into context. The survey allows us to address some questions related to the prevalence and properties of planetesimal systems. Methods. We used Herschel/PACS to observe a sample of nearby FGK stars. Data at 100 and 160 μm were obtained, complemented in some cases with observations at 70 μm, and at 250, 350 and 500 μm using SPIRE. The observing strategy was to integrate as deep as possible at 100 μm to detect the stellar photosphere. Results. Debris discs have been detected at a fractional luminosity level down to several times that of the Edgeworth-Kuiper belt. The incidence rate of discs around the DUNES stars is increased from a rate of ~12.1% ± 5% before Herschel to ~20.2% ± 2%. A significant fraction (~52%) of the discs are resolved, which represents an enormous step ahead from the previously known resolved discs. Some stars are associated with faint far-IR excesses attributed to a new class of cold discs. Although it cannot be excluded that these excesses are produced by coincidental alignment of background galaxies, statistical arguments suggest that at least some of them are true debris discs. Some discs display peculiar SEDs with spectral indexes in the 70–160 μm range steeper than the Rayleigh-Jeans one. An analysis of the debris disc parameters suggests that a decrease might exist of the mean black body radius from the F-type to the K-type stars. In addition, a weak trend is suggested for a correlation of disc sizes and an anticorrelation of disc temperatures with the stellar age.
ABSTRACT Debris discs are typically revealed through the presence of excess emission at infrared wavelengths. Most discs exhibit excess at mid- and far-infrared wavelengths, analogous to the solar ...system's Asteroid and Edgeworth-Kuiper belts. Recently, stars with strong (∼1%) excess at near-infrared wavelengths were identified through interferometric measurements. Using the HIgh Precision Polarimetric Instrument, we examined a sub-sample of these hot dust stars (and appropriate controls) at parts-per-million sensitivity in SDSS g′ (green) and r′ (red) filters for evidence of scattered light. No detection of strongly polarized emission from the hot dust stars is seen. We, therefore, rule out scattered light from a normal debris disk as the origin of this emission. A wavelength-dependent contribution from multiple dust components for hot dust stars is inferred from the dispersion (the difference in polarization angle in red and green) of southern stars. Contributions of 17 ppm (green) and 30 ppm (red) are calculated, with strict 3- upper limits of 76 and 68 ppm, respectively. This suggests weak hot dust excesses consistent with thermal emission, although we cannot rule out contrived scenarios, e.g., dust in a spherical shell or face-on discs. We also report on the nature of the local interstellar medium (ISM), obtained as a byproduct of the control measurements. Highlights include the first measurements of the polarimetric color of the local ISM and the discovery of a southern sky region with a polarization per distance thrice the previous maximum. The data suggest that λmax, the wavelength of maximum polarization, is bluer than typical.
Abstract
Gamma-ray bursts (GRBs) have been classified traditionally based on their duration. The increasing number of extended emission (EE) GRBs, lasting typically more than 2s but with properties ...similar to those of short GRBs, challenges the traditional classification criteria. In this work, we use the t-distributed stochastic neighbor embedding (t-SNE), a machine-learning technique, to classify GRBs. We present the results for GRBs observed until 2022 July by the Swift/BAT (Burst Alert Telescope) instrument in all its energy bands. We show the effects of varying the learning rate and perplexity parameters as well as the benefit of preprocessing the data by a nonparametric noise-reduction technique. Consistently with previous works, we show that the t-SNE method separates GRBs into two subgroups. We also show that EE GRBs reported by various authors under different criteria tend to cluster in a few regions of our t-SNE maps and identify seven new EE GRB candidates by using the gamma-ray data provided by the automatic pipeline of Swift/BAT and the proximity with previously identified EE GRBs.
Retention is a key element in HIV prevention programs. In Sub-Saharan Africa most data on retention come from HIV clinical trials or people living with HIV attending HIV treatment and control ...programs. Data from observational cohorts are less frequent. Retention at 6-/12-month follow-up and its predictors were analyzed in OKAPI prospective cohort. From April 2016 to April 2018, 797 participants aged 15-59 years attending HIV Voluntary Counseling and Testing in Kinshasa were interviewed about HIV-related knowledge and behaviors at baseline and at 6- and 12-month follow-ups. Retention rates were 57% and 27% at 6- and 12-month follow up; 22% of participants attended both visits. Retention at 6-month was significantly associated with 12-month retention. Retention was associated with low economic status, being studying, daily/weekly Internet access, previous HIV tests and aiming to share HIV test with partner. Contrarily, perceiving a good health, living far from an antiretroviral center, daily/weekly alcohol consumption and perceiving frequent HIV information were inversely associated with retention. In conclusion, a high attrition was found among people attending HIV testing participating in a prospective cohort in Kinshasa. Considering the low retention rates and the predictors found in this study, more HIV cohort studies in Kinshasa need to be evaluated to identify local factors and strategies that could improve retention if needed.
We present the homogeneous analysis of a sample of Southern early-type M dwarfs in the solar neighborhood (d < 60 pc). We used the MCAL technique to derive the effective temperature Teff, metallicity ...Fe/H, and activity index ia(Halpha) of 420 M stars using HARPS spectra. The effective temperature Teff, surface gravity log g, metallicity Fe/H, and projected rotational velocity Vrotsini of 153 M0-M6 dwarfs were determined by fitting the observed intermediate-resolution spectra from the VIS arm of VLT/X-shooter with a grid of BT-Settl stellar atmosphere models. We estimated the typical uncertainties of the fit with X-shooter spectra by varying region-to-region results by Teff ∼ 50 K, log g ∼ 0.2, and Fe/H ∼ 0.2 dex. Photometric verification of Teff for the 295 stars from the HARPS sample and the 61 stars from the X-shooter sample is also provided. We compared our results from different methods to estimate absolute uncertainty in determining the physical properties of M dwarfs.
ABSTRACT
We report on the high-resolution spectroscopic observations of two planetary transits of the hot Jupiter KELT-7b (Mp = 1.28 ± 0.17MJup, Teq = 2028 K) observed with the High Optical ...Resolution Spectrograph (HORuS) mounted on the 10.4-m Gran Telescopio Canarias (GTC). A new set of stellar parameters are obtained for the rapidly rotating parent star from the analysis of the spectra. Using the newly derived stellar mass and radius, and the planetary transit data of the Transiting Exoplanet Survey Satellite (TESS) together with the HORuS velocities and the photometric and spectroscopic data available in the literature, we update and improve the ephemeris of KELT-7b. Our results indicate that KELT-7 has an angle λ = −10.55 ± 0.27 deg between the sky projections of the star’s spin axis and the planet’s orbital axis. By combining this angle and our newly derived stellar rotation period of 1.38 ± 0.05 d, we obtained a 3D obliquity ψ = 12.4 ± 11.7 deg (or 167.6 deg), thus reinforcing that KELT-7 is a well-aligned planetary system. We search for the presence of Hα, Li i, Na i, Mg i, and Ca ii features in the transmission spectrum of KELT-7b but we are only able to determine upper limits of 0.08–1.4 per cent on their presence after accounting for the contribution of the stellar variability to the extracted planetary spectrum. We also discuss the impact of stellar variability on the planetary data. Our results reinforce the importance of monitoring the parent star when performing high-resolution transmission spectroscopy of the planetary atmosphere in the presence of stellar activity.
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