- ID:
- ivo://CDS.VizieR/J/A+A/466/157
- Title:
- Bulge Microlensing Events
- Short Name:
- J/A+A/466/157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Microlensing events have been observed regularly by surveys such as MACHO, OGLE and MOA. They offer an excellent way to probe the galactic structure, kinematics and stellar content. We have undertaken a follow-up study of 16 galactic microlensing events to determine masses and locations of the sources of these events within the Galaxy. Spectroscopy allows us to obtain information about the sources of the events. Low resolution spectra obtained with the Magellan I and II telescopes were analyzed to obtain radial velocities, spectral type and extinction by the method of Kane & Sahu (2003ApJ...582..743K). We also present results for the lens of the event using the microlensing light curve when possible. Light curves have been analyzed with the standard and the parallax models. We have inferred a configuration inside our galaxy for each event, and therefore a lens mass estimation using a suitable galaxy model. Lens mass determination in some cases shows massive lenses that can be considered black hole candidates. This is the case for the events MACHO-98-BLG-6, and OGLE-00-BUL-43. In our sample only three events do not have enough parallax signal for a successful estimation of the lens mass.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/821/L25
- Title:
- Bulge RR Lyrae Radial Velocity Assay (BRAVA-RR)
- Short Name:
- J/ApJ/821/L25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 947 radial velocities of RR Lyrae variable stars in four fields located toward the Galactic bulge, observed within the data from the ongoing Bulge RR Lyrae Radial Velocity Assay (BRAVA-RR). We show that these RR Lyrae stars (RRLs) exhibit hot kinematics and null or negligible rotation and are therefore members of a separate population from the bar/pseudobulge that currently dominates the mass and luminosity of the inner Galaxy. Our RRLs predate these structures and have metallicities, kinematics, and spatial distribution that are consistent with a "classical" bulge, although we cannot yet completely rule out the possibility that they are the metal-poor tail of a more metal-rich ([Fe/H]~-1dex) halo-bulge population.
- ID:
- ivo://CDS.VizieR/J/other/ApSS/363.127
- Title:
- Bulge RR Lyrae VVVDR4 photometry
- Short Name:
- J/other/ApSS/363
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study's objective was to exploit infrared VVV (VISTA Variables in the Via Lactea) photometry for high latitude RRab stars to establish an accurate Galactic Centre distance. RRab candidates were discovered and reaffirmed (n=4194) by matching Ks photometry with templates via chisq minimization, and contaminants were reduced by ensuring targets adhered to a strict period-amplitude (Ks) trend and passed the Elorietta et al. (2016A&A...595A..82E) classifier. The distance to the Galactic Centre was determined from a high latitude Bulge subsample (|b|>4, RGC=8.30+/-0.36kpc, random uncertainty is relatively negligible), and importantly, the comparatively low color-excess and uncrowded location mitigated uncertainties tied to the extinction law, the magnitude-limited nature of the analysis, and photometric contamination. Circumventing those problems resulted in a key uncertainty being the MKs relation, which was derived using LMC RRab stars (MKs=-(2.66+/-0.06)logP-(1.03+/-0.06), (J-Ks)0=(0.31+/-0.04)logP +(0.35+/-0.02), assuming mu0LMC=18.43). The Galactic Centre distance was not corrected for the cone-effect. Lastly, a new distance indicator emerged as brighter overdensities in the period-magnitude-amplitude diagrams analyzed, which arise from blended RRab and red clump stars. Blending may thrust faint extragalactic variables into the range of detectability.
2124. Bulge SC1 proper motions
- ID:
- ivo://CDS.VizieR/J/MNRAS/340/1346
- Title:
- Bulge SC1 proper motions
- Short Name:
- J/MNRAS/340/1346
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report a measurement of the streaming motion of the stars in the Galactic bar with the red clump giants (RCGs) using the data of the Optical Gravitational Lensing Experiment II (OGLE-II). We measure the proper motion of 46961 stars and divide RCGs into bright and faint subsamples that on average will be closer to the near and far sides of the bar, respectively. We find that the far-side RCGs (4979 stars) have a proper motion of {Delta}<{mu}>~1.5+/-0.11mas/yr toward the negative longitudes relative to the near-side RCGs (3610 stars).
- ID:
- ivo://CDS.VizieR/J/ApJ/716/942
- Title:
- Bulges of nearby galaxies with Spitzer
- Short Name:
- J/ApJ/716/942
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate scaling relations of bulges using bulge-disk decompositions at 3.6um and present bulge classifications for 173 E-Sd galaxies within 20Mpc. Pseudobulges and classical bulges are identified using Sersic index, Hubble Space Telescope morphology, and star formation activity (traced by 8um emission). In the near-IR pseudobulges have n_b_<2 and classical bulges have n_b_>2, as found in the optical. Sersic index and morphology are essentially equivalent properties for bulge classification purposes. We confirm, using a much more robust sample, that the Sersic index of pseudobulges is uncorrelated with other bulge structural properties, unlike for classical bulges and elliptical galaxies. Also, the half-light radius of pseudobulges is not correlated with any other bulge property. We also find a new correlation between surface brightness and pseudobulge luminosity; pseudobulges become more luminous as they become more dense.
- ID:
- ivo://CDS.VizieR/J/A+A/609/A112
- Title:
- Bulk Lorentz factors of gamma-ray bursts
- Short Name:
- J/A+A/609/A112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Knowledge of the bulk Lorentz factor {Gamma}_0_ of gamma-ray bursts (GRBs) allows us to compute their comoving frame properties shedding light on their physics. Upon collisions with the circumburst matter, the fireball of a GRB starts to decelerate, producing a peak or a break (depending on the circumburst density profile) in the light curve of the afterglow. Considering all bursts with known redshift and with an early coverage of their emission, we find 67 GRBs (including one short event) with a peak in their optical or GeV light curves at a time t_p_. For another 106 GRBs we set an upper limit t_p_^UL^. The measure of t_p_ provides the bulk Lorentz factor {Gamma}_0_ of the fireball before deceleration. We show that t_p_ is due to the dynamics of the fireball deceleration and not to the passage of a characteristic frequency of the synchrotron spectrum across the optical band. Considering the t_p_ of 66 long GRBs and the 85 most constraining upper limits, we estimate {Gamma}_0_ or a lower limit {Gamma}_0_^LL^. Using censored data analysis methods, we reconstruct the most likely distribution of t_p_. All t_p_ are larger than the time T_p,{gamma}_ when the prompt {gamma}-ray emission peaks, and are much larger than the time T_ph_ when the fireball becomes transparent, that is, t_p_>T_p,{gamma}_>T_ph_. The reconstructed distribution of {Gamma}_0_ has median value ~300 (150) for a uniform (wind) circumburst density profile. In the comoving frame, long GRBs have typical isotropic energy, luminosity, and peak energy <E_iso_>=3(8)x10^50^erg, <L_iso_>=3(15)x10^47^erg/s, and <E_peak_>=1(2)keV in the homogeneous (wind) case. We confirm that the significant correlations between {Gamma}_0_ and the rest frame isotropic energy (E_iso_), luminosity (L_iso_), and peak energy (E_p_) are not due to selection effects. When combined, they lead to the observed E_p_-E_iso_ and E_p_-L_iso_ correlations. Finally, assuming a typical opening angle of 5 degrees, we derive the distribution of the jet baryon loading which is centered around a few 10^-6^M_{\sun}_.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A121
- Title:
- Buoyancy radius of {gamma} Dor stars
- Short Name:
- J/A+A/626/A121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Helioseismology and asteroseismology of red giant stars have shown that distribution of angular momentum in stellar interiors, and the evolution of this distribution with time remains an open issue in stellar physics. Owing to the unprecedented quality and long baseline of Kepler photometry, we are able to seismically infer internal rotation rates in {gamma} Doradus stars, which provide the main-sequence counterpart to the red-giants puzzle. Here, we confront these internal rotation rates to stellar evolution models which account for rotationally induced transport of angular momentum, in order to test angular momentum transport mechanisms. On the one hand, we used a stellar model-independent method developed by our team in order to obtain accurate, seismically inferred, buoyancy radii and near-core rotation for 37 {gamma} Doradus stars observed by Kepler. We show that the stellar buoyancy radius can be used as a reliable evolution indicator for field stars on the main sequence. On the other hand, we computed rotating evolutionary models of intermediate-mass stars including internal transport of angular momentum in radiative zones, following the formalism developed in the series of papers started by Zahn (1992A&A...265..115Z), with the cestam code. This code calculates the rotational history of stars from the birth line to the tip of the RGB. The initial angular momentum content has to be set initially, which is done here by fitting rotation periods in young stellar clusters. We show a clear disagreement between the near-core rotation rates measured in the sample and the rotation rates obtained from the evolutionary models including rotationally induced transport of angular momentum following Zahn's prescriptions. These results show a disagreement similar to that of the Sun and red giant stars in the considered mass range. This suggests the existence of missing mechanisms responsible for the braking of the core before and along the main sequence. The efficiency of the missing mechanisms is investigated. The transport of angular momentum as formalized by Zahn and Maeder cannot explain the measurements of near-core rotation in main-sequence intermediate-mass stars we have at hand.
- ID:
- ivo://CDS.VizieR/J/AJ/142/2
- Title:
- Burrell-Optical-Kepler-Survey (BOKS). I.
- Short Name:
- J/AJ/142/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the initial results of a 40 night contiguous ground-based campaign of time series photometric observations of a 1.39deg^2^ field located within the NASA Kepler Mission field of view. The goal of this pre-launch survey was to search for transiting extrasolar planets and to provide independent variability information of stellar sources. We have gathered a data set containing light curves of 54,687 stars from which we have created a statistical sub-sample of 13,786 stars between 14<r<18.5 and have statistically examined each light curve to test for variability. We present a summary of our preliminary photometric findings including the overall level and content of stellar variability in this portion of the Kepler field and give some examples of unusual variable stars found within. We present a preliminary catalog of 2,457 candidate variable stars, of which 776 show signs of periodicity. We also present three potential exoplanet candidates, all of which should be observable by the Kepler mission.
- ID:
- ivo://CDS.VizieR/J/ApJ/787/66
- Title:
- Burst duration measurements for a GRB sample
- Short Name:
- J/ApJ/787/66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Several gamma-ray bursts (GRBs) last much longer (~hours) in {gamma}-rays than typical long GRBs (~minutes), and it has recently been proposed that these "ultra-long GRBs" may form a distinct population, probably with a different (e.g., blue supergiant) progenitor than typical GRBs. However, Swift observations suggest that many GRBs have extended central engine activities manifested as flares and internal plateaus in X-rays. We perform a comprehensive study on a large sample of Swift GRBs with X-Ray Telescope observations to investigate GRB central engine activity duration and to determine whether ultra-long GRBs are unusual events. We define burst duration t_burst_ based on both {gamma}-ray and X-ray light curves rather than using {gamma}-ray observations alone. We find that t_burst_can be reliably measured in 343 GRBs. Within this "good" sample, 21.9% GRBs have t_burst_>~10^3^ s and 11.5% GRBs have t_burst_>~10^4^ s. There is an apparent bimodal distribution of t_burst_ in this sample. However, when we consider an "undetermined" sample (304 GRBs) with t_burst_ possibly falling in the gap between GRB duration T_90_ and the first X-ray observational time, as well as a selection effect against t_burst_ falling into the first Swift orbital "dead zone" due to observation constraints, the intrinsic underlying t_burst_ distribution is consistent with being a single component distribution. We found that the existing evidence for a separate ultra-long GRB population is inconclusive, and further multi-wavelength observations are needed to draw a firmer conclusion. We also discuss the theoretical implications of our results. In particular, the central engine activity duration of GRBs is generally much longer than the {gamma}-ray T_90_ duration and it does not even correlate with T_90_. It would be premature to make a direct connection between T_90_ and the size of the progenitor star.
2130. Butterfly diagram wings
- ID:
- ivo://CDS.VizieR/J/A+A/599/A131
- Title:
- Butterfly diagram wings
- Short Name:
- J/A+A/599/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The continuous spatio-temporal evolution (the so-called 'Maunder butterfly diagram') of sunspot activity was available since 1874 using data from the Royal Greenwich Observatory since 1875, extended by SOON network data after 1976. Here we present a new extended butterfly diagram of sunspot group occurrence continuously since 1826, using the recently digitized data from Schwabe (1826-1867) and Spoerer (1868-1874). The wings of the diagram are separated using a recently developed method based on long gaps in sunspot group occurrence in different latitude bands. Characteristic latitudes, corresponding to the start, end and the latitudinal span of the wings, F-, L- and H-latitudes, respectively, as well as times and asymmetries of the butterfly wings are analyzed. The F-latitude depict a weak tendency, especially in the S-hemisphere, to follow the wing strength (quantified in the total sum of monthly numbers of sunspot groups). The H-latitudes are highly significantly correlated with the strength of the wings during cycles 12-23. The L-latitudes show no clear relation to the wing strength. Overall, stronger cycle wings tend to start at higher latitudes and have greater wing's span. A strong (5-6)-cycle periodic oscillation was found in many latitudinal parameters, such as dates of the start and end of the wings and, most pronounced, in the difference between the wing lengths in the two hemispheres. A barely significant oscillation of about 10 cycles period is found in the asymmetry of the L-latitudes. The new long database of butterfly wings and the results based on it provide new observational constraints to the spatio-temporal distribution of sunspot occurrence and their solar cycle related time-latitude evolution.
