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5251. Polarization of 125 stars in NGC 1817 open cluster
ID:
ivo://CDS.VizieR/J/AJ/160/256
Title:
Polarization of 125 stars in NGC 1817 open cluster
Short Name:
J/AJ/160/256
Date:
21 Oct 2021
Publisher:
CDS
Description:
Multiband linear polarimetric observations of 125 stars in the region of the cluster NGC1817 have been carried out intending to study properties of interstellar dust and grains in that direction. The polarization is found to be wavelength-dependent, being maximum in the V-band with an average value of 0.95%. The foreground interstellar dust grains appear to be the main source of linear polarization of starlight toward the direction of NGC1817. The average value of the position angle in the V-band of 119.2{deg} is found to be less than the direction of the Galactic parallel in the region, indicating that the dust grains in the direction are probably not yet relaxed. Spatial distribution of dust appears to be more diverse in the coronal region than the core region of the cluster. The maximum value of the degree of polarization is estimated to be 0.93% for members of the cluster using the Serkowski relation. The average value of wavelength corresponding to the maximum polarization of 0.54{+/-}0.02{mu}m indicates that the size distribution of dust grains in the line of sight is similar to that of the general interstellar medium. Several variable stars in the cluster were also observed polarimetrically and pulsating variables appear to have a slightly lower value of polarization from other nonvariable member stars of the cluster. There are indications of the existence of dust layers in front of those clusters which are located close to galactic plane while for clusters located away from galactic plane no major dust layers are observed.
5252. Polarization & photom. of stars toward LDN1225
ID:
ivo://CDS.VizieR/J/ApJ/875/64
Title:
Polarization & photom. of stars toward LDN1225
Short Name:
J/ApJ/875/64
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results based on the optical R-band observations of the polarization of 280 stars distributed toward the dark globule LDN1225. Parallaxes from Gaia data release 2 along with the polarization data of ~200 stars have been used to (a) constrain the distance of LDN 1225 as 830+/-83pc, (b) determine the contribution of interstellar polarization, and (c) characterize the dust properties and delineate the magnetic field (B-field) morphology of LDN 1225. We find that B-fields are more organized and exhibit a small dispersion of 12{deg}. Using the ^12^CO molecular line data from the Purple Mountain Observatory, along with the column density and dispersion in B-fields, we estimate the B-field strength to be ~56+/-10{mu}G, the ratio of magnetic to turbulent pressure to be ~3+/-2, and the ratio of mass to magnetic flux (in units of the critical value) to be <1. These results indicate the dominant role of B-fields in comparison to turbulence and gravity in rendering the cloud support. B-fields are aligned parallel to the low-density parts (traced by a ^12^CO map) of the cloud; in contrast, they are neither parallel nor perpendicular to the high-density core structures (traced by ^13^CO and C^18^O maps). LDN1225 hosts two 70{mu}m sources, which seem to be low-mass Class 0 sources. The ratio of total to selective extinction derived using optical and near-infrared photometric data is found to be anomalous (RV=3.4), suggesting the growth of dust grains in LDN 1225. The polarization efficiency of dust grains follows a power law with an index of -0.7, implying that optical polarimetry traces B-fields in the outer parts of the cloud.
5253. PopStar I: Evolutionary synthesis models
ID:
ivo://CDS.VizieR/J/MNRAS/398/451
Title:
PopStar I: Evolutionary synthesis models
Short Name:
J/MNRAS/398/451
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new evolutionary synthesis models for Simple Stellar Populations for a wide range of ages and metallicities. The models are based on the Padova isochrones. The core of the spectral library is provided by the medium resolution Lejeune et al. atmosphere models. These spectra are complemented by NLTE atmosphere models for hot stars that have an important impact in the stellar cluster's ionizing spectra: O, B and WR stellar spectra at the early ages, and spectra of post-AGB stars and planetary nebulae, at intermediate and old ages. At young ages, our models compare well with other existing models but we find that, the inclusion of the nebular continuum, not considered in several other models, reddens significantly the integrated colours of very young stellar populations. This is consistent with the results of spectral synthesis codes particularly devised for the study of starburst galaxies. At intermediate and old ages, the agreement with literature model is good and, in particular, we reproduce well the observed colours of star clusters in LMC. Given the ability to produce good integrated spectra from the far-UV to the infrared at any age, we consider that our models are particularly suited for the study of high redshift galaxies. These models are available on the web site http://www.fractal-es.com/SEDmod.htm and also through the Virtual Observatory Tools on the PopStar server.
5254. POPSTAR models. III. Young star clusters
ID:
ivo://CDS.VizieR/J/MNRAS/432/2746
Title:
POPSTAR models. III. Young star clusters
Short Name:
J/MNRAS/432/2746
Date:
21 Oct 2021
Publisher:
CDS
Description:
This is the third paper of a series reporting the results from the POPSTAR evolutionary synthesis models. The main goal of this work is to present and discuss the synthetic photometric properties of single stellar populations resulting from our POPSTAR code. Colours in the Johnson and Sloan Digital Sky Survey (SDSS) systems, H{alpha} and H{beta} luminosities and equivalent widths, and ionizing region size, have been computed for a wide range of metallicity (Z=0.0001-0.05) and age (0.1Myr to 20Gyr). We calculate the evolution of the cluster and the region geometry in a consistent manner. We demonstrate the importance of the contribution of emission lines to broader band photometry when characterizing stellar populations, through the presentation of both contaminated and non-contaminated colours (in both the Johnson and SDSS systems). The tabulated colours include stellar and nebular components, in addition to line emission. The main application of these models is the determination of physical properties of a given young ionizing cluster, when only photometric observations are available; for an isolated star-forming region, the young star cluster models can be used, free from the contamination of any underlying background stellar population. In most cases, however, the ionizing population is usually embedded in a large and complex system, and the observed photometric properties result from the combination of a young star-forming burst and the underlying older population of the host. Therefore, the second objective of this paper is to provide a grid of models useful in the interpretation of mixed regions where the separation of young and old populations is not sufficiently reliable. We describe the set of popstar spectral energy distributions (SEDs), and the derived colours for mixed populations where an underlying host population is combined in different mass-ratios with a recent ionizing burst. These colours, together with other common photometric parameters, such as the H{alpha} radius of the ionized region, and Balmer line equivalent widths and luminosities, allow one to infer the physical properties of star-forming regions even in the absence of spectroscopic information.
5255. Position and photometry of stars in SDIG
ID:
ivo://CDS.VizieR/J/A+A/549/A47
Title:
Position and photometry of stars in SDIG
Short Name:
J/A+A/549/A47
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the resolved stellar populations and derive the star formation history of the Sculptor dwarf irregular galaxy (SDIG), a gas-rich dwarf galaxy member of the NGC 7793 subgroup in the Sculptor group of galaxies. We constructed a colour - magnitude diagram (CMD) using archival observations from the Hubble Space Telescope/Advanced Camera for Surveys in order to examine the stellar content of SDIG, as well as the spatial distribution of stars selected within different stellar evolutionary phases. We derived the star formation history of SDIG using a maximum-likelihood fit to the CMD.
5256. Positions and space velocities for 2615 SGP stars
ID:
ivo://CDS.VizieR/J/AJ/126/762
Title:
Positions and space velocities for 2615 SGP stars
Short Name:
J/AJ/126/762
Date:
21 Oct 2021
Publisher:
CDS
Description:
Spectrophotometric data have been obtained with the 2dF spectrograph at Cerro Tololo Inter-American Observatory and with Hydra at the WIYN telescope for nearly 2000 A, F, and G stars toward the south Galactic pole. Using 1305 radial velocities, 2311 uvbyH{beta} photometric measurements, and 1621 Yale-San Juan SPM (Southern Proper Motion) absolute proper motions, peculiar velocities were derived to determine the galactic gravitational force K(z) perpendicular to the Galactic plane, first described by Oort (published in 1932).
5257. Positions of giant radio galaxies
ID:
ivo://CDS.VizieR/J/A+A/374/861
Title:
Positions of giant radio galaxies
Short Name:
J/A+A/374/861
Date:
21 Oct 2021
Publisher:
CDS
Description:
In tablea1.dat, we present the WENSS selected candidate GRGs after removing sources identified as non-GRGs on basis of optical data. In tablea2.dat, we present the log of the spectroscopic observations of GRG andidates in our sample. In tablea3.dat, we present properties of the radio cores and the optical identifications of the spectroscopically observed giant radio sources, and of the confirmed giant sources B1144+352, B1245+676 and B1310+451. We provide the name of the radio source in IAU notation, the observation used to determine the radio core position and its flux density and the radio core position in right ascension and declination, respectively, in B1950.0 coordinates. The radio positions have been obtained by fitting a Gaussian in the radio map. We further provide the integrated flux density at 1.4GHz of the radio core, the position of the optical identification in right ascension and declination, respectively, in B1950.0 coordinates, obtained from fitting a Gaussian in the available optical image and the magnitude of the identification in the red (POSS-E) band of the Palomar survey. The magnitudes for sources weaker than 15.0 have been obtained from the APM catalogue and are estimated to be accurate to 0.5 mag. For brighter sources, we have measured the magnitudes directly from the digitized POSS-I frames using the photometric calibration for stars available from the STScI WWW-pages and through the getimage-2.0 plate retrieval software. Typical uncertainties in these values are estimated to be large, at least 1mag. In tablea4.dat, further radio properties of the sources in tablea3.dat. We present the integrated flux density of the source at 325MHz from the Westerbork Northern Sky Survey (WENSS) (unless stated otherwise), the integrated flux density at 1400MHz from the NVSS, the spectral index between 325 and 1400MHz, the redshift of the host galaxy, the angular size of the radio source in arcminutes, the resulting projected linear size in Mpc (using H_0=50km/s/Mpc, q_0_=0.5) and the radio luminosity at an emitted frequency of 325MHz.
5258. Post-AGB/RGB and YSOs in SMC
ID:
ivo://CDS.VizieR/J/MNRAS/439/2211
Title:
Post-AGB/RGB and YSOs in SMC
Short Name:
J/MNRAS/439/2211
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have carried out a search for optically visible post-asymptotic giant branch (post-AGB) candidates in the Small Magellanic Cloud (SMC). First, we used mid-IR observations from the Spitzer Space Telescope to select optically visible candidates with excess mid-IR flux and then we obtained low-resolution optical spectra for 801 of the candidates. After removing poor-quality spectra and contaminants, such as M-stars, C-stars, planetary nebulae, quasi-stellar objects and background galaxies, we ended up with a final sample of 63 high-probability post-AGB/RGB candidates of A-F spectral type. From the spectral observations, we estimated the stellar parameters: effective temperature (T_eff_), surface gravity (logg) and metallicity ([Fe/H]). We also estimated the reddening and deduced the luminosity using the stellar parameters combined with photometry. For the post-AGB/RGB candidates, we found that the metallicity distribution peaks at [Fe/H]~-1.00dex. Based on a luminosity criterion, 42 of these 63 sources were classified as post-red giant branch (post-RGB) candidates and the remaining 21 as post-AGB candidates. From the spectral energy distributions, we were able to infer that 6 of the 63 post-AGB/RGB candidates have a surrounding circumstellar shell suggesting that they are single stars, while 27 of the post-AGB/RGB candidates have a surrounding disc, suggesting that they lie in binary systems. For the remaining 30 post-AGB/RGB candidates the nature of the circumstellar environment was unclear. Variability is displayed by 38 of the 63 post-AGB/RGB candidates with the most common variability types being the Population II Cepheids (including RV-Tauri stars) and semiregular variables. This study has also revealed a new RV Tauri star in the SMC, J005107.19-734133.3, which shows signs of s-process enrichment. From the numbers of post-AGB/RGB stars in the SMC, we were able to estimate evolutionary rates. We find that the number of post-AGB and post-RGB candidates that we have identified are in good agreement with the stellar evolution models with some mass-loss in the post-AGB phase and a small amount of re-accretion in the lower luminosity post-RGB phase. This study also resulted in a new sample of 40 young stellar objects (YSOs) of A-F spectral type. The 40 YSO candidates for which we could estimate stellar parameters are luminous and of high mass (~3-10M_{sun}_). They lie on the cool side of the usually adopted birthline in the HR-diagram. This line separates visually obscured protostars from optically visible pre-main-sequence stars, meaning that our YSO candidates have become optically visible in the region of the HR diagram usually reserved for obscured protostars. Additionally, we also identified a group of 63 objects whose spectra are dominated by emission lines and in some cases, a significant UV continuum. These objects are very likely to be either hot post-AGB/RGB candidates or luminous YSOs.
5259. Post-common-envelope PN and mol. mass
ID:
ivo://CDS.VizieR/J/A+A/658/A17
Title:
Post-common-envelope PN and mol. mass
Short Name:
J/A+A/658/A17
Date:
21 Mar 2022 09:39:31
Publisher:
CDS
Description:
Most planetary nebulae (PNe) show beautiful, axisymmetric morphologies despite their progenitor stars being essentially spherical. Close binarity is widely invoked to help eject an axisymmetric nebula, after a brief phase of engulfment of the secondary within the envelope of the Asymptotic Giant Branch (AGB) star, known as the common envelope (CE). The evolution of the AGB would thus be interrupted abruptly, its still quite massive envelope being rapidly ejected to form the PN, which a priori would be more massive than a PN coming from the same star, were it single. We aim at testing this hypothesis by investigating the ionised and molecular masses of a sample consisting of 21 post-CE PNe, roughly one fifth of the known total population of these objects, and comparing them to a large sample of 'regular' (i.e. not known to arise from close-binary systems) PNe. We have gathered data on the ionised and molecular content of our sample from the literature, and carried out molecular observations of several previously unobserved objects. We derive the ionised and molecular masses of the sample by means of a systematic approach, using tabulated, dereddened H-beta fluxes for finding the ionised mass, and ^12^CO J=2-1 and J=3-2 observations for estimating the molecular mass. There is a general lack of molecular content in post-CE PNe. Our observations only reveal molecule-rich gas around NGC 6778, distributed into a low-mass, expanding equatorial ring lying beyond the ionised broken ring previously observed in this nebula. The only two other objects showing molecular content (from the literature) are NGC 2346 and NGC 7293. Once we derive the ionised and molecular masses, we find that post-CE PNe arising from Single-Degenerate (SD) systems are just as massive, on average, as the 'regular' PNe sample, whereas post-CE PNe arising from Double-Degenerate (DD) systems are considerably more massive, and show substantially larger linear momenta and kinetic energy than SD systems and `regular' PNe. Reconstruction of the CE of four objects, for which a wealth of data on the nebulae and complete orbital parameters are available, further suggests that the mass of SD nebulae actually amounts to a very small fraction of the envelope of their progenitor stars. This leads to the uncomfortable question of where the rest of the envelope is and why we cannot detect it in the stars' vicinity, thus raising serious doubts on our understanding of these intriguing objects.
5260. Post-merger cluster A2255 membership
ID:
ivo://CDS.VizieR/J/ApJ/794/31
Title:
Post-merger cluster A2255 membership
Short Name:
J/ApJ/794/31
Date:
21 Oct 2021
Publisher:
CDS
Description:
The effects of dense environments on normal field galaxies are still up for debate despite much study since Abell published his catalog of nearby clusters in 1958 (1958ApJS....3..211A). There are changes in color, morphology, and star formation properties when galaxies fall into groups and clusters, but the specifics of how and where these modifications occur are not fully understood. To look for answers, we focused on star-forming galaxies in A2255, an unrelaxed cluster thought to have recently experienced a merger with another cluster or large group. We used H{alpha}, MIPS 24 {mu}m, and WISE 22 {mu}m to estimate total star formation rates (SFRs) and Sloan Digital Sky Survey photometry to find stellar masses (M_*_) for galaxies out to ~5 r_200_. We compared the star-forming cluster galaxies with the field SFR-mass distribution and found no enhancement or suppression of star formation in currently star-forming galaxies of high mass (log(M_*_/M_{sun}_)>~10). This conclusion holds out to very large distances from the cluster center. However, the core (r_proj_<3 Mpc) has a much lower fraction of star-forming galaxies than anywhere else in the cluster. These results indicate that for the mass range studied here, the majority of the star formation suppression occurs in the core on relatively short timescales, without any enhancement prior to entering the central region. If any significant enhancement or quenching of star formation occurs, it will be in galaxies of lower mass (log(M_*_/M_{sun}_)<10).