- 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.
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Search Results
- 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.
2174. 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.
- ID:
- ivo://CDS.VizieR/J/A+A/357/471
- Title:
- BV and proper motions in NGC 1960 & NGC 2194
- Short Name:
- J/A+A/357/471
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD photometry and proper motion studies of the two open star clusters NGC 1960 (M 36) and NGC 2194. Fitting isochrones to the colour magnitude diagrams, for NGC 1960 we found an age of 16Myr and a distance of roughly 1300 pc and for NGC 2194 550Myr and 2900pc, respectively. We combined membership determination by proper motions and statistical field star subtraction to derive the initial mass function of the clusters and found slopes of -1.23+/-0.17 for NGC 1960 and -1.33+/-0.29 for NGC 2194. Compared to other IMF studies of the intermediate mass range, these values indicate shallow mass functions. These tables present the complete data of the photometry (Tables 2 and 3) and the proper motion studies (Tables 7 and 9) of the two clusters.
- ID:
- ivo://CDS.VizieR/J/A+A/611/A69
- Title:
- B,V and R band polarimetry of lambda Tau
- Short Name:
- J/A+A/611/A69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Linear polarization measurements of lambda Tau in the B, V and R passbands with the high-precision Dipol-2 polarimeter have been carried out. The data have been obtained on the 60cm KVA (Observatory Roque de los Muchachos, La Palma, Spain) and Tohoku 60cm (Haleakala, Hawaii, USA) remotely controlled telescopes during 69 observing nights. Optical polarimetry revealed small intrinsic polarization with ~0.05% peak to peak variation over the orbital period of ~3.95d. Variability pattern is typical for binary systems showing strong second harmonic of the orbital period. We apply a standard analytical method and our own light scattering models to derive parameters of the inner binary orbit from the fit to the observed variability of the normalized Stokes parameters. Analytic and numerical modelling codes are used to interpret the data.
- ID:
- ivo://CDS.VizieR/J/A+AS/121/499
- Title:
- BV and rg photometry of Pal 13
- Short Name:
- J/A+AS/121/499
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new CCD photometry of the halo cluster Palomar 13 is used to construct a color-magnitude diagram in the Thuan-Gunn and the B, V photometric systems. The color-magnitude diagram of the cluster shows as already noted by Ortolani et al. (1985AJ.....90..473O) an extremely poor red horizontal branch and a very sparsely populated giant branch. Seven BSS candidates are identified in the field of Palomar 13. The age of the cluster determined by fitting with the isochrones of Proffitt & Vanden Berg (1991ApJS...77..473P) and Bergbusch & Vanden Berg (1992ApJS...81..163B) and by a differential comparison of the color-magnitude diagram with that of Pal 5 is 12+/-2Gyr.
- ID:
- ivo://CDS.VizieR/J/ApJ/780/L25
- Title:
- 1898-2013 BV and visual photometry for V603 Aql
- Short Name:
- J/ApJ/780/L25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the light curve of the old nova V603 Aql (Nova Aql 1918) from 1898-1918 and 1934-2013 using 22721 archival magnitudes. All of our magnitudes are either in, or accurately transformed into, the Johnson B and V magnitude systems. This is vital because offsets in old sequences and the visual-to-V transformation can cause errors of 0.1-1.0mag if not corrected. Our V603 Aql light curve is the first time that this has been done for any nova. Our goal was to see the evolution of the mass accretion rate on a century timescale, and to test the long-standing prediction of the Hibernation model that old novae should be fading significantly in the century after their eruption is over. The 1918 nova eruption was completely finished by 1938 when the nova decline stopped, and when the star had faded to fainter than its pre-nova brightness of B=11.43+/-0.03mag. We find that the nova light from 1938 to 2013 was significantly fading, with this being seen consistently in three independent data sets (the Sonneberg plates in B, the American Association of Variable Star Observers (AAVSO) V light curve, and the non-AAVSO V light curve). We find that V603 Aql has been declining in brightness at an average rate of 0.44+/-0.04mag per century since 1938. This work provides remarkable confirmation of an important prediction of the Hibernation model.
- ID:
- ivo://CDS.VizieR/J/A+A/463/981
- Title:
- BV CCD photometry in Westerlund 2
- Short Name:
- J/A+A/463/981
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The properties of the early-type stars in the core of the Westerlund 2 cluster are examined in order to establish a link between the cluster and the very massive Wolf-Rayet binary WR20a as well as the H II complex RCW 49. Photometric monitoring as well as spectroscopic observations of Westerlund 2 are used to search for light variability and to establish the spectral types of the early-type stars in the cluster core. The first light curves of the eclipsing binary WR 20a in B and V filters are analysed and a distance of 8kpc is inferred. Three additional eclipsing binaries, which are probable late O or early B-type cluster members, are discovered, but none of the known early O-type stars in the cluster displays significant photometric variability above 1% at the 1-sigma level. The twelve brightest O-type stars are found to have spectral types between O3 and O6.5, significantly earlier than previously thought. The distance of the early-type stars in Westerlund 2 is established to be in excellent agreement with the distance of WR20a, indicating that WR20a actually belongs to the cluster. Our best estimate of the cluster distance thus amounts to 8.0+/-1.4kpc. Despite the earlier spectral types, the currently known population of early-type stars in Westerlund 2 does not provide enough ionizing photons to account for the radio emission of the RCW 49 complex. This suggests that there might still exist a number of embedded early O-stars in RCW49.
- ID:
- ivo://CDS.VizieR/J/PASP/104/1063
- Title:
- BV Color-Magnitude Diagram for NGC 1851
- Short Name:
- J/PASP/104/1063
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- BV photometry is provided for 1,234 stars in the magnitude range 13-18 in an annulus between 5 and 20 arc seconds from the center of NGC 1851 and for 1,247 stars in the magnitude range 18-23 at a distance of more than 240 arc seconds from the center. For stars in the magnitude range 16-21, the errors in B-V increase with magnitude from 0.005 mag. to 0.022 mag. See the document file (walker.txt or walker.tex) by Nancy G. Roman for more details.
