Analysis of 746 new V-band observations of the RR Lyrae star AH Cam obtained during 1989-1992 clearly show that its light curve cannot be described by a single period. In fact, at first glance, the Fourier spectrum of the photometry resembles that of a double-mode pulsator, with peaks at a fundamental period of 0.3686d and an apparent secondary period of 0.2628d. Nevertheless, the dual-mode solution is a poor fit to the data. Rather, we believe that AH Cam is a single-mode RR Lyrae star undergoing the Blazhko effect: periodic modulation of the amplitude and shape of its light curve. What was originally taken to be the period of the second mode is instead the 1-cycle/d alias of a modulation sidelobe in the Fourier spectrum. The data are well described by a modulation period of just under 11d, which is the shortest Blazhko period reported to date in the literature and confirms the earlier suggestion by Goranskii. A low-resolution spectrum of AH Cam indicates that it is relatively metal rich, with {DELTA}S<=2. Its high metallicity and short modulation period may provide a critical test of at least one theory for the Blazhko effect. Moskalik's internal resonance model makes specific predictions of the growth rate of the fundamental mode vs fundamental period. AH Cam falls outside the regime of other known Blazhko variables and resonance model predictions, but these are appropriate for metal-poor RR Lyrae stars. If the theory matches the behavior of AH Cam for a metal-rich stellar model, this would bolster the resonance hypothesis.
Hipparcos trigonometric parallaxes fix distances to individual stars in the Hyades cluster with an accuracy of about 6 percent. We use the Hipparcos and Tycho-2 proper motions, which have a larger relative precision than the Hipparcos trigonometric parallaxes, to derive 3 times more precise distance estimates, by assuming that all members share the same space motion. These so-called secular parallaxes are, as a set, statistically consistent with the Hipparcos parallaxes (Section 6). Table A1 contains, for all 218 members identified by Perryman et al. (1998A&A...331...81P; see also Cat. <J/A+A/331/81>; see Sections 4.1 and 5.1), the trigonometric parallaxes, the Hipparcos and Tycho-2 secular parallaxes, their errors and goodness-of-fit parameters (Sections 2.2 and 5.4), as well as fundamental stellar parameters (Section 9) based on the Hipparcos secular parallaxes and the V-band magnitudes (field H5) and B-V colours (field H37) listed in the Hipparcos Catalogue (1997HIP...C......0E; Cat. <I/239>). Table A2 lists 15 new Hyades candidates (see Sections 4.2 and 5.2) selected by the membership methods developed by de Bruijne (1999MNRAS.306..381D) and Hoogerwerf et al. (1999MNRAS.306..394H) which use proper motion and trigonometric parallax data. Based on photometric, radial velocity, and secular parallax data, we conclude that only one of these stars (HIP 19757) is a likely new member (see Sections 4.2 and 5.2 for details).
This is the first paper in a series aimed at defining a statistically significant sample of QSOs in the range 15<B<18.75 and 0.3<z<2.2. The selection is carried out using direct plates obtained at the ESO and UK Schmidt Telescopes, scanned with the COSMOS facility and searched for objects with an ultraviolet excess. Follow-up spectroscopy, carried out at ESO La Silla, is used to classify each candidate. In this initial paper, we describe the scientific objectives of the survey; the selection and observing techniques used. We present the first sample of 285 QSOs (M_B_<-23) in a 153 sq.deg area, covered by the six "deep" fields, intended to obtain significant statistics down B=~18.75 with unprecedented photometric accuracy. From this database, QSO counts are determined in the magnitude range 17<B<18.75.
We present a new method to test the {Lambda}CDM cosmological model and to estimate cosmological parameters based on the nonlinear relation between the ultraviolet and X-ray luminosities of quasars. We built a data set of 1138 quasars by merging several samples from the literature with X-ray measurements at 2keV and SDSS photometry, which was used to estimate the extinction-corrected 2500{AA} flux. We obtained three main results: (1) we checked the nonlinear relation between X-ray and UV luminosities in small redshift bins up to z~6, confirming that the relation holds at all redshifts with the same slope; (2) we built a Hubble diagram for quasars up to z~6, which is well matched to that of supernovae in the common z=0-1.4 redshift interval and extends the test of the cosmological model up to z~6; and (3) we showed that this nonlinear relation is a powerful tool for estimating cosmological parameters. Using the present data and assuming a {Lambda}CDM model, we obtain {Omega}_M_=0.22_-0.08_^+0.10^ and {Omega}_{Lambda}_=0.92-0.30_^+0.18^ ({Omega}=0.28+/-0.04 and {Omega}_{Lambda}_=0.73+/-0.08 from a joint quasar-SNe fit). Much more precise measurements will be achieved with future surveys. A few thousand SDSS quasars already have serendipitous X-ray observations from Chandra or XMM-Newton, and at least 100000 quasars with UV and X-ray data will be made available by the extended ROentgen Survey with an Imaging Telescope Array all-sky survey in a few years. The Euclid, Large Synoptic Survey Telescope, and Advanced Telescope for High ENergy Astrophysics surveys will further increase the sample size to at least several hundred thousand. Our simulations show that these samples will provide tight constraints on the cosmological parameters and will allow us to test for possible deviations from the standard model with higher precision than is possible today.
Stellar Department of Astronomical Institute of the Academy of
Sciences of the Czech Republic
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Stellar Department of Astronomical Institute of the Academy of
Sciences of the Czech Republic
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Tables exposed through this endpoint include: objcat, objects_observed, objobs_complete, objobs_lightcurves, observation_info from the bextract schema, dim_exposure, dim_observation_objcat, exposure, objcat, objobs_complete, objobs_lightcurves, observation, observation_objcat from the bextract_jan16 schema, reduced_images from the dk154_reduced schema, exposure, objcat, objobs_complete, objobs_lightcurves, observation from the bextract_jan15 schema, columns, groups, key_columns, keys, schemas, tables from the tap_schema schema, dim_exposure, dim_observation_objcat, exposure, objcat, objobs_complete, objobs_lightcurves, objobs_lightcurves_ssap, observation, observation_objcat from the bextract_apr18 schema, data from the ccd700 schema, dim_exposure, dim_observation_objcat, exposure, objcat, objobs_complete, objobs_lightcurves, observation, observation_objcat from the bextract_jan15_v2 schema, emptyobscore, obscore from the ivoa schema, data from the heros schema, reduced_images from the dk154_reduced_jan18 schema, dim_exposure, dim_observation_objcat, exposure, objcat, objobs_complete, objobs_lightcurves, observation, observation_objcat from the bextract_jul15 schema, dim_exposure, dim_observation_objcat, exposure, objcat, objobs_complete, objobs_lightcurves, objobs_lightcurves_ssap, observation, observation_objcat from the bextract_jul16 schema, data from the lamost_dr2 schema, data from the lamost_dr3 schema, data from the lamost schema, data from the lamost_dr1 schema, dim_exposure, dim_observation_objcat, exposure, objcat, objobs_complete, objobs_lightcurves, objobs_lightcurves_ssap, observation, observation_objcat from the bextract_jan18 schema, dim_exposure, dim_observation_objcat, exposure, objcat, objobs_complete, objobs_lightcurves, objobs_lightcurves_ssap, observation, observation_objcat from the bextract_dec17 schema, raw_images from the dk154_rawdata schema.
The U BV photometry and low-resolution spectroscopy for the semiregular variable AI CMi, a candidate for post-AGB objects, performed in 1996-2016 and 2000-2013, respectively, are presented. The star showed multiperiodic brightness variations with an amplitude up to 1.5m in the V band, a significant (up to 0.4m) bluing of the B-V and U-B colors as the star faded, and a change of its spectrum from G5 I to K3-5 I, depending on its brightness. A possible long-term fading of AI CMi below 8.5m in the period from May 2013 to early 2015 is observed in the light curve. The colors in this episode did not change the pattern of their unusual behavior with brightness. The main feature of the spectrum for AI CMi is the appearance and strengthening of TiO absorption bands as its brightness declines, which are atypical in the spectra of ordinary G5-K3 supergiants. The bluing of the B-V and U-B colors is interpreted as the blanketing of stellar radiation predominantly in V (and to a lesser extent in B) by the TiO absorption bands whose intensity increases dramatically with decreasing brightness. Another cause of the bluing can be the scattering of stellar radiation by small dust particles in the gas-dust shell of AI CMi. The star's continuum-normalized spectra over the period from 2000 to 2013 in the wavelength range 4200 to 7700 or 9200{AA} are presented. These were taken at different phases of the pulsation cycle and clearly demonstrate the behavior of the TiO absorption bands depending on the V magnitude and B-V color. The equivalent widths of individual TiO bands were measured, and their correlation with the photometric parameters of the star is shown. AI CMi belongs to the O-rich branch of AGB/post-AGB supergiants and has a luminosity of ~4000L_{sun}_ at a distance of 1500+/-700pc. The mass of AI CMi is most likely small and close to the lower mass limit for post-AGB stars. The connection of the star's pulsational activity and nonstationary wind with the formation of its molecular and dust shells is discussed briefly.
We describe the structural and kinematic properties of the first compact stellar systems discovered by the Archive of Intermediate Mass Stellar Systems project. These spectroscopically confirmed objects have sizes (~6<R_e_[pc]<500) and masses (~2x10^6^<M*/M_{sun}_<6x10^9^) spanning the range of massive globular clusters, ultracompact dwarfs (UCDs) and compact elliptical galaxies (cEs), completely filling the gap between star clusters and galaxies. Several objects are close analogues to the prototypical cE, M32. These objects, which are more massive than previously discovered UCDs of the same size, further call into question the existence of a tight mass-size trend for compact stellar systems, while simultaneously strengthening the case for a universal 'zone of avoidance' for dynamically hot stellar systems in the mass-size plane. Overall, we argue that there are two classes of compact stellar systems (1) massive star clusters and (2) a population closely related to galaxies. Our data provide indications for a further division of the galaxy-type UCD/cE population into two groups, one population that we associate with objects formed by the stripping of nucleated dwarf galaxies, and a second population that formed through the stripping of bulged galaxies or are lower mass analogues of classical ellipticals. We find compact stellar systems around galaxies in low- to high-density environments, demonstrating that the physical processes responsible for forming them do not only operate in the densest clusters.
![To the extent possible under law, the publisher has waived all copyright and related or neighboring rights to GAVO's ADQL course. For details, see the `Creative Commons CC0 1.0 Public Domain dedication <http://creativecommons.org/publicdomain/zero/1.0/>`_. Of course, you should still give proper credit when using this data as required by good scientific practice. .. image:: /static/img/cc0.png :alt: [CC0]](/registry-search/?f%5Brights_facet%5D%5B%5D=To+the+extent+possible+under+law%2C+the+publisher+has+waived+all+copyright+and+related+or+neighboring+rights+to+GAVO%27s+ADQL+course.++For+details%2C+see+the+%60Creative+Commons+CC0+1.0+Public+Domain+dedication+%3Chttp%3A%2F%2Fcreativecommons.org%2Fpublicdomain%2Fzero%2F1.0%2F%3E%60_.++Of+course%2C+you+should+still+give+proper+credit+when+using+this+data+as+required+by+good+scientific+practice.%0A%0A..+image%3A%3A+%2Fstatic%2Fimg%2Fcc0.png%0A+++%3Aalt%3A+%5BCC0%5D%0A%0A&f%5Btype_facet%5D%5B%5D=%0A++++++++++++&f%5BvalidationLevel_facet%5D%5B%5D=2){kind=link}