- ID:
- ivo://CDS.VizieR/J/A+A/631/A48
- Title:
- rho Cas differential BVRI photometry
- Short Name:
- J/A+A/631/A48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to explore the variable photometric and stellar properties of four yellow hypergiants (YHGs), HR 8752, HR 5171A, rho Cas, and HD 179821, and their pulsations of hundreds of days, and long-term variations (LTVs) of years. We also aim to explore light and colour curves for characteristics betraying evolutionary loops and eruptive episodes and to investigate trends of quasi-periods and the possible need for distance revisions. We tackled multi-colour and visual photometric data sets, looked for photometric indications betraying eruptions or enhanced mass-loss episodes, calculated stellar properties mainly using a previously published temperature calibration, and investigated the nature of LTVs and their influence on quasi-periods and stellar properties. Based on driven one-zone stellar oscillation models, the pulsations can be characterised as 'weakly chaotic'. The BV photometry revealed a high-opacity layer in the atmospheres. When the temperature rises the mass loss increases as well, consequently, as the density of the high-opacity layer. As a result, the absorption in B and V grow. The absorption in B, presumably of the order of one to a few 0.1mag, is always higher than in V. This difference renders redder and variable (B-V) colour indexes, but the absorption law is unknown. This property of YHGs is unpredictable and explains why spectroscopic temperatures (reddening independent) are always higher than photometric ones, but the difference decreases with the temperature. A new (weak) eruption of rho Cas has been identified. We propose shorter distances for rho Cas and HR 5171A than the accepted ones. Therefore, a correction to decrease the blue luminescence of HR 5171A by polycyclic aromatic hydrocarbon (PAH) molecules is necessary, and HR 5171A would no longer be a member of the cluster Gum48d. HR 5171A is only subject to one source of light variation, not by two as the literature suggests. Eruptive episodes (lasting one to two years), of YHGs prefer relatively cool circumstances when a red evolutionary loop (RL) has shifted the star to the red on the HR diagram. After the eruption, a blue loop evolution (BL) is triggered lasting one to a few decades. We claim that in addition to HR 8752, also the other three YHGs have shown similar cycles over the last 70 years. This supports the suspicion that HD 179821 might be a YHG (with a possible eruptive episode between 1925 and 1960). The range in temperature of these cyclic Teff variations is 3000K-4000K. LTVs mainly consist of such BL and RL evolutions, which are responsible for a decrease and increase, respectively, of the quasi-periods. The reddening episode of HR 5171A between 1960 and 1974 was most likely due to a red loop evolution, and the reddening after the 1975 eruption was likely due to a shell ejection, taking place simultaneously with a blue loop evolution.
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- ID:
- ivo://CDS.VizieR/J/AN/325/705
- Title:
- RIJHKs of low-mass stars in sigma Ori
- Short Name:
- J/AN/325/705
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an RI photometric survey covering an area of 430 arcmin^2^ around the multiple star sigma Orionis. The observations were conducted with the 0.8m IAC-80 Telescope at the Teide Observatory. The survey limiting R and I magnitudes are 22.5 and 21, and completeness magnitudes 21 and 20, respectively. We have selected 53 candidates from the I vs. R-I colour-magnitude diagram (I=14-20) that follow the previously known photometric sequence of the cluster. Adopting an age of 2-4 Myr for the cluster, we find that these objects span a mass range from 0.35M_{sun}_ to 0.015M_{sun}_. We have performed J-band photometry of 52 candidates and K_s photometry for 12 of them, with the result that 50 follow the expected infrared sequence for the cluster, thus confirming with great confidence that the majority of the candidates are bona fide members. JHK_s photometry from the Two Micron All Sky Survey (2MASS, Cat. <II/246>) is available for 50 of the candidates and are in good agreement with our data. Out of 48 candidates, which have photometric accuracies better than 0.1mag in all bands, only three appear to show near-infrared excesses.
- ID:
- ivo://CDS.VizieR/J/ApJS/202/19
- Title:
- riz photometry in Cyg OB2
- Short Name:
- J/ApJS/202/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to fully understand the gravitational collapse of molecular clouds, the star formation process, and the evolution of circumstellar disks, these phenomena must be studied in different Galactic environments with a range of stellar contents and positions in the Galaxy. The young massive association Cygnus OB2, in the Cygnus-X region, is a unique target to study how star formation and the evolution of circumstellar disks proceed in the presence of a large number of massive stars. We present a catalog obtained with recent optical observations in the r, i, z filters with OSIRIS, mounted on the 10.4m Gran Telescopio CANARIAS telescope, which is the deepest optical catalog of CygOB2 to date. The catalog consists of 64,157 sources down to M=0.15M_{sun}_ at the adopted distance and age of Cyg OB2. A total of 38,300 sources have good photometry in all three bands. We combined the optical catalog with existing X-ray data of this region, in order to define the cluster locus in the optical diagrams. The cluster locus in the r-i versus i-z diagram is compatible with an extinction of the optically selected cluster members in the 2.64m<A_V_<5.57m range. We derive an extinction map of the region, finding a median value of A_V_=4.33m in the center of the association, decreasing toward the northwest. In the color-magnitude diagrams, the shape of the distribution of main-sequence stars is compatible with the presence of an obscuring cloud in the foreground ~850+/-25pc from the Sun.
- ID:
- ivo://CDS.VizieR/J/A+A/346/586
- Title:
- Rotating models of A and F stars
- Short Name:
- J/A+A/346/586
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Magnitude differences between rotating and non-rotating copartners for a grid of models with solar metallicity are tabulated here. The results are expressed in terms of the dimensionless angular velocity w-bar- defined in Eq.(1) of the paper, the angle of inclination i and the atmospheric parameters T_e_ and g_e_ defined in Eqs.(22) and (21), respectively. To obtain the absolute magnitudes for a given rotating model, the magnitudes of a non-rotating model with T_eff_=T_e_, g=g_e_ and the same intrinsic luminosity must be added. Results are given for the filters in the Geneva, Johnson and Stroemgren systems. Eq (1): w-bar = {Omega}/{Omega}_c_, where {Omega} is the angular velocity of the star, and {Omega}_c_^2^=8GM/(27R^3^_p_), where M is the mass and R_p_ the polar radius.
- ID:
- ivo://CDS.VizieR/J/ApJ/874/30
- Title:
- RRab stars toward Baade's window with Blanco/DECam
- Short Name:
- J/ApJ/874/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained repeated images of six fields toward the Galactic bulge in five passbands (u, g, r, i, z) with the DECam imager on the Blanco 4m telescope at CTIO. From more than 1.6 billion individual photometric measurements in the field centered on Baade's window, we have detected 4877 putative variable stars. A total of 474 of these have been confirmed as fundamental mode RR Lyrae stars, whose colors at minimum light yield line-of-sight reddening determinations, as well as a reddenning law toward the Galactic Bulge, which differs significantly from the standard R_V_=3.1 formulation. Assuming that the stellar mix is invariant over the 3 square-degree field, we are able to derive a line-of-sight reddening map with sub-arcminute resolution, enabling us to obtain de-reddened and extinction corrected color-magnitude diagrams (CMDs) of this bulge field using up to 2.5 million well-measured stars. The corrected CMDs show unprecedented detail and expose sparsely populated sequences: for example, delineation of the very wide red giant branch, structure within the red giant clump, the full extent of the horizontal branch, and a surprising bright feature that is likely due to stars with ages younger than 1Gyr. We use the RR Lyrae stars to trace the spatial structure of the ancient stars and find an exponential decline in density with Galactocentric distance. We discuss ways in which our data products can be used to explore the age and metallicity properties of the bulge, and how our larger list of all variables is useful for learning to interpret future LSST alerts.
- ID:
- ivo://CDS.VizieR/J/A+A/430/1049
- Title:
- RR Gem BV(RI)c differential photometry
- Short Name:
- J/A+A/430/1049
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Extended CCD monitoring of RR Gem revealed that it is a Blazhko type RRab star with the shortest Blazhko period (7.23d) and smallest modulation amplitude (delta_Mmax_<0.1mag) currently known. The short period of the modulation cycle enabled us to obtain complete phase coverage of the pulsation at each phase of the modulation. This is the first multicolour observation of a Blazhko star which is extended enough to define accurate mean magnitudes and colours of the variable at different Blazhko phases. Small, but real, changes in the intensity mean colours at different Blazhko phases have been detected. The Fourier analysis of the light curves shows that, in spite of the mmag and smaller order of the amplitudes, the triplet structure is noticeable up to about the 14th harmonic. The modulation is concentrated to a very narrow, 0.2 phase range of the pulsation, centred on the supposed onset of the H emission during rising light. These observational results raise further complications for theoretical explanation of the long known but poorly understood Blazhko phenomenon.
- ID:
- ivo://CDS.VizieR/J/AJ/152/170
- Title:
- RRLs in globulars. IV. UBVRI photometry in Omega Cen
- Short Name:
- J/AJ/152/170
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New accurate and homogeneous optical UBVRI photometry has been obtained for variable stars in the Galactic globular cluster {omega} Cen (NGC 5139). We secured 8202 CCD images covering a time interval of 24 years and a sky area of 84x48arcmin. The current data were complemented with data available in the literature and provided new, homogeneous pulsation parameters (mean magnitudes, luminosity amplitudes, periods) for 187 candidate {omega} Cen RR Lyrae (RRLs). Among them we have 101 RRc (first overtone) and 85 RRab (fundamental) variables, and a single candidate RRd (double-mode) variable. Candidate Blazhko RRLs show periods and colors that are intermediate between the RRc and RRab variables, suggesting that they are transitional objects. A comparison of the period distribution and the Bailey diagram indicates that RRLs in {omega} Cen show a long-period tail not present in typical Oosterhoff II (OoII) globulars. The RRLs in dwarf spheroidals and in ultra-faint dwarfs have properties between Oosterhoff intermediate and OoII clusters. Metallicity plays a key role in shaping the above evidence. These findings do not support the hypothesis that {omega} Cen is the core remnant of a spoiled dwarf galaxy. Using optical period-Wesenheit relations that are reddening-free and minimally dependent on metallicity we find a mean distance to {omega} Cen of 13.71+/-0.08+/-0.01mag (semi-empirical and theoretical calibrations). Finally, we invert the I-band period-luminosity-metallicity relation to estimate individual RRLs' metal abundances. The metallicity distribution agrees quite well with spectroscopic and photometric metallicity estimates available in the literature.
- ID:
- ivo://CDS.VizieR/J/AJ/155/137
- Title:
- RRLs in globulars. V.{omega} Centauri NIR photometry
- Short Name:
- J/AJ/155/137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new complete near-infrared (NIR, JHK_s_) census of RR Lyrae stars (RRLs) in the globular {omega} Cen (NGC 5139). We collected 15472 JHK_s_ images with 4-8 m class telescopes over 15 years (2000-2015) covering a sky area around the cluster center of 60x34 arcmin^2^. These images provided calibrated photometry for 182 out of the 198 cluster RRL candidates with 10 to 60 measurements per band. We also provide new homogeneous estimates of the photometric amplitude for 180 (J), 176 (H) and 174 (K_s_) RRLs. These data were supplemented with single-epoch JK_s_ magnitudes from VHS (Mcmahon et al. 2013Msngr.154...35M) and with single-epoch H magnitudes from 2MASS (Cat. VII/233). Using proprietary optical and NIR data together with new optical light curves (ASAS-SN) we also updated pulsation periods for 59 candidate RRLs. As a whole, we provide JHK_s_ magnitudes for 90 RRab (fundamentals), 103 RRc (first overtones) and one RRd (mixed-mode pulsator). We found that NIR/optical photometric amplitude ratios increase when moving from first overtone to fundamental and to long-period (P>0.7 days) fundamental RRLs. Using predicted period-luminosity-metallicity relations, we derive a true distance modulus of 13.674+/-0.008+/-0.038 mag (statistical error and standard deviation of the median) based on spectroscopic iron abundances, and of 13.698+/-0.004+/-0.048 mag based on photometric iron abundances. We also found evidence of possible systematics at the 5%-10% level in the zero-point of the period-luminosity relations based on the five calibrating RRLs whose parallaxes had been determined with the HST.
- ID:
- ivo://CDS.VizieR/J/AJ/140/1766
- Title:
- RR Lyrae in M62 (NGC6266)
- Short Name:
- J/AJ/140/1766
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new time-series CCD photometry, in the B and V bands, for the moderately metal-rich ([Fe/H]=~-1.3) Galactic globular cluster M62 (NGC 6266). The present data set is the largest obtained so far for this cluster and consists of 168 images per filter, obtained with the Warsaw 1.3m telescope at the Las Campanas Observatory and the 1.3m telescope of the Cerro Tololo Inter-American Observatory, in two separate runs over the time span of 3 months.
- ID:
- ivo://CDS.VizieR/J/AJ/158/223
- Title:
- RR Lyrae members of the Pal 5 stellar stream
- Short Name:
- J/AJ/158/223
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Thin stellar streams, formed from the tidal disruption of globular clusters, are important gravitational tools, sensitive to both global and small-scale properties of dark matter. The Palomar 5 stellar stream (Pal 5) is an exemplar stream within the Milky Way: its ~20{deg} tidal tails connect back to the progenitor cluster, and the stream has been used to study the shape, total mass, and substructure fraction of the dark matter distribution of the Galaxy. However, most details of the phase-space distribution of the stream are not fully explained, and dynamical models that use the stream for other inferences are therefore incomplete. Here we aim to measure distance and kinematic properties along the Pal 5 stream in order to motivate improved models of the system. We use a large catalog of RR Lyrae-type stars (RRLs) with astrometric data from the Gaia mission to probabilistically identify RRLs in the Pal 5 stream. RRLs are useful because they are intrinsically luminous standard candles and their distances can be inferred with small relative precision (~3%). By building a probabilistic model of the Pal 5 cluster and stream in proper motion and distance, we find 27 RRLs consistent with being members of the cluster (10) and stream (17). Using these RRLs, we detect gradients in distance and proper motion along the stream, and provide an updated measurement of the distance to the Pal 5 cluster using the RRLs, d=20.6+/-0.2 kpc. We provide a catalog of Pal 5 RRLs with inferred membership probabilities for future modeling work.
