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1271. Ori OB1 CP stars magnetic fields. V.
ID:
ivo://CDS.VizieR/J/other/AstBu/76.163
Title:
Ori OB1 CP stars magnetic fields. V.
Short Name:
J/other/AstBu/76
Date:
21 Oct 2021
Publisher:
CDS
Description:
The paper presents the results of magnetic field measurements of 27 chemically peculiar stars in subgroups (c) and (d) of the Orion OB1 association. In total, more than 140 circularly polarized spectra were obtained and measured in the period from 2013 to 2020. An analysis of the results showed that 13 out of 24 CP stars in subgroup (c) have a magnetic field. At the same time, no field of a significant strength was found in any of the three CP stars in subgroup (d). We found that the occurrence of magnetic stars in subgroup (c), whose average age is approximately 5Myr, lies in the middle between the occurrence of magnetic stars in subgroups (a) with an age of 10 Myr and (b), whose age is about 2Myr. Our results indicate a sharp decrease in the occurrence of magnetic CP stars and a simultaneous decrease in their magnetic field with age. The data obtained with the example of the Orion OB1 association generally support the theory of the fossil origin of the magnetic field of chemically peculiar stars; however, the process of the field formation itself can have a number of features manifesting observationally.
1272. Ori OB1 CP stars magnetic fields. V.
ID:
ivo://CDS.VizieR/J/other/AstBu/76.39
Title:
Ori OB1 CP stars magnetic fields. V.
Short Name:
J/other/AstBu/76
Date:
21 Oct 2021
Publisher:
CDS
Description:
The paper presents magnetic field measurements for 15 chemically peculiar (CP) stars of subgroup 1b in the Orion OB1 association. We have found that the proportion of stars with strong magnetic fields among these 15 CP stars is almost twice as large as in subgroup 1a. Along with this, the age of subgroup 1b is estimated as 2Myr, and the age of subgroup 1a is in the order of 10Myr. The average root-mean-square magnetic field <Be> (all) for stars in subgroup 1b is 2.3 times higher than that for stars in subgroup 1a. The conclusions obtained fall within the concept of the fossil origin of large-scale magnetic fields in B and A stars, but the rate of field weakening with age appears anomalously high. We present our results as an important observational test for calibrating the theory of stellar magnetic field formation and evolution.
1273. Orion Bar photon-dominated region water lines
ID:
ivo://CDS.VizieR/J/A+A/632/A8
Title:
Orion Bar photon-dominated region water lines
Short Name:
J/A+A/632/A8
Date:
21 Oct 2021
Publisher:
CDS
Description:
The ortho-to-para ratio (OPR) of water in the interstellar medium (ISM) is often assumed to be related to the formation temperature of water molecules, making it a potentially interesting tracer of the thermal history of interstellar gas. A very low OPR of 0.1-0.5 was previously reported in the Orion Bar photon-dominated region (PDR), based on observations of two optically thin H_2_^18^O lines which were analyzed by using a single-slab large velocity gradient (LVG) model. The corresponding spin temperature does not coincide with the kinetic temperature of the molecular gas in this UV-illuminated region. This was interpreted as an indication of water molecules being formed on cold icy grains which were subsequently released by UV photodesorption. A more complete set of water observations in the Orion Bar, including seven H_2_^16^O lines and one H_2_^18^O line, carried out using Herschel/HIFI instrument, was reanalyzed using the Meudon PDR code to derive gas-phase water abundance and the OPR. The model takes into account the steep density and temperature gradients present in the region. The model line intensities are in good agreement with the observations assuming that water molecules formed with an OPR corresponding to thermal equilibrium conditions at the local kinetic temperature of the gas and when solely considering gas-phase chemistry and water gas-grain exchanges through adsorption and desorption. Gas-phase water is predicted to arise from a region deep into the cloud, corresponding to a visual extinction of A_V_~9, with a H_2_^16^O fractional abundance of ~2x10^-7^ and column density of (1.4+/-0.8)x10^15^cm^-2^ for a total cloud depth of A_V_=15. A line-of-sight average OPR of 2.8+/-0.2 is derived. The observational data are consistent with a nuclear spin isomer repartition corresponding to the thermal equilibrium at a temperature of 36+/-2K, much higher than the spin temperature previously reported for this region and close to the gas kinetic temperature in the water-emitting gas.
1274. Oscillations of red giants observed by Kepler
ID:
ivo://CDS.VizieR/J/A+A/540/A143
Title:
Oscillations of red giants observed by Kepler
Short Name:
J/A+A/540/A143
Date:
21 Oct 2021
Publisher:
CDS
Description:
There are now more than 22 months of long-cadence data available for thousands of red giants observed with the Kepler space mission. Consequently, we are able to clearly resolve fine details in their oscillation spectra and see many components of the mixed modes that probe the stellar core. We report for the first time a parametric fit to the pattern of the l=1 mixed modes in red giants, which is a powerful tool to identify gravity-dominated mixed modes. With these modes, which share the characteristics of pressure and gravity modes, we are able to probe directly the helium core and the surrounding shell where hydrogen is burning.
1275. OSMOS & modspec RVs of 30 cataclysmic variables
ID:
ivo://CDS.VizieR/J/AJ/160/6
Title:
OSMOS & modspec RVs of 30 cataclysmic variables
Short Name:
J/AJ/160/6
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present spectroscopy and orbital periods Porb for 30 apparently nonmagnetic cataclysmic binaries with periods below ~3hr, nearly all of which are dwarf novae, mostly of the SU Ursae Majoris subclass. We then turn to the evidence supporting the prediction that short-period dwarf novae evolve toward longer periods after passing through a minimum period-the "period bounce" phenomenon. Plotting data from the literature reveals that for superhump period excess {epsilon}=(P_sh_-P_orb_)/P_orb_ below ~0.015, the period appears to increase with decreasing {epsilon}, agreeing at least qualitatively with the predicted behavior. Next, motivated by the long (decadal) outburst intervals of the WZ Sagittae subclass of short-period dwarf novae, we ask whether there could be a sizable population of "lurkers"-systems that resemble dwarf novae at minimum light, but which do not outburst over accessible timescales (or at all) and therefore do not draw attention to themselves. By examining the outburst history of the Sloan Digital Sky Survey sample of Cataclysmic Variables (CVs), which were selected by color and not by outburst, we find that a large majority of the color-selected dwarf-nova-like objects have been observed to outburst, and we conclude that "lurkers," if they exist, are a relatively minor part of the CV population.
1276. Outburst of V1318 Cyg S (LkHa 225)
ID:
ivo://CDS.VizieR/J/A+A/625/A13
Title:
Outburst of V1318 Cyg S (LkHa 225)
Short Name:
J/A+A/625/A13
Date:
21 Oct 2021
Publisher:
CDS
Description:
Young double star V1318 Cyg, which is associated with a small isolated star-forming region around HAeBe star BD+40 4124, has very unusual photometric and spectral behavior. We present results of photometric and spectroscopic observations in the optical range. We carried out BVRI CCD photometric observations of V1318 Cyg from 2015 Sept. to 2017 July. For the same period we acquired medium- and low-resolution spectra. Observations were performed with the 2.6 m telescope of the Byurakan observatory. We also analyzed the images of this field in IPHAS and other surveys. We analyze the historical light curve for V1318 Cyg and demonstrate that the southern component, V1318 Cyg S, after being rather bright in the 1970s (V~14 mag) started to lower its brightness and in 1990 became practically invisible in the optical. After its reappearance in the second half of the 1990s the star started to become very slowly brighter. Between 2006 and 2010 V1318 Cyg S started brightening more quickly, and in 2015 had become brighter by more than five magnitudes in visible light. Since this time V1318 Cyg S has remained at this maximum. Its spectrum shows little variability and consists of a mixture of emission and absorption lines, which has allowed for estimates of its spectral type as early Ae, with obvious evidence of matter outflow. We derive its current A(V)~7.2 and L=750L_(sun)_ thus confirming that V1318 Cyg S should belong to the Herbig Ae stars, making it, along with BD+40 4124 and V1686 Cyg, the third luminous young star in the group. It is very probable that we observe V1318 Cyg S near the pole and that the inclination of its dense and slow (<100km/s) outflow is low. The unusual variability and other features of V1318 Cyg S make it difficult to classify this star among known types of eruptive young stars. It could be an extreme, higher-mass example of an EXor, or an object of intermediate class between EXors and FUors, like V1647 Ori.
1277. Outflows in sodium excess objects
ID:
ivo://CDS.VizieR/J/ApJ/809/91
Title:
Outflows in sodium excess objects
Short Name:
J/ApJ/809/91
Date:
21 Oct 2021
Publisher:
CDS
Description:
Van Dokkum and Conroy (2010Natur.468..940V) revisited the unexpectedly strong NaI lines at 8200{AA} found in some giant elliptical galaxies and interpreted them as evidence for an unusually bottom-heavy initial mass function. Jeong et al. (2013, J/ApJS/208/7) later found a large population of galaxies showing equally extraordinary Na D doublet absorption lines at 5900{AA} (Na D excess objects: NEOs) and showed that their origins can be different for different types of galaxies. While a Na D excess seems to be related to the interstellar medium (ISM) in late-type galaxies, smooth-looking early-type NEOs show little or no dust extinction and hence no compelling signs of ISM contributions. To further test this finding, we measured the Doppler components in the Na D lines. We hypothesized that the ISM would have a better (albeit not definite) chance of showing a blueshift Doppler departure from the bulk of the stellar population due to outflow caused by either star formation or AGN activities. Many of the late-type NEOs clearly show blueshift in their Na D lines, which is consistent with the former interpretation that the Na D excess found in them is related to gas outflow caused by star formation. On the contrary, smooth-looking early-type NEOs do not show any notable Doppler components, which is also consistent with the interpretation of Jeong et al. that the Na D excess in early-type NEOs is likely not related to ISM activities but is purely stellar in origin.
1278. Outliers and similarity in APOGEE
ID:
ivo://CDS.VizieR/J/MNRAS/476/2117
Title:
Outliers and similarity in APOGEE
Short Name:
J/MNRAS/476/2117
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this work we apply and expand on a recently introduced outlier detection algorithm that is based on an unsupervised random forest. We use the algorithm to calculate a similarity measure for stellar spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE). We show that the similarity measure traces non-trivial physical properties and contains information about complex structures in the data. We use it for visualization and clustering of the dataset, and discuss its ability to find groups of highly similar objects, including spectroscopic twins. Using the similarity matrix to search the dataset for objects allows us to find objects that are impossible to find using their best fitting model parameters. This includes extreme objects for which the models fail, and rare objects that are outside the scope of the model. We use the similarity measure to detect outliers in the dataset, and find a number of previously unknown Be-type stars, spectroscopic binaries, carbon rich stars, young stars, and a few that we cannot interpret. Our work further demonstrates the potential for scientific discovery when combining machine learning methods with modern survey data.
1279. Oxygen abundance in M83
ID:
ivo://CDS.VizieR/J/ApJ/695/580
Title:
Oxygen abundance in M83
Short Name:
J/ApJ/695/580
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have obtained deep multiobject optical spectra of 49 HII regions in the outer disk of the spiral galaxy M83 (=NGC 5236) with the FORS2 spectrograph at the Very Large Telescope. The targets span the range in galactocentric distance between 0.64 and 2.64 times the R_25_ isophotal radius (5.4-22.3kpc), and 31 of them are located at R>R_25_, thus belonging to the extreme outer disk of the galaxy, populated by UV complexes revealed recently by the Galaxy Evolution Explorer satellite. In order to derive the nebular chemical abundances, we apply several diagnostics of the oxygen abundance, including R_23_, [NII]/[OII], and the [OIII]{lambda}4363 auroral line, which was detected in four HII regions.
1280. Oxygen abundances for giant HII regions in NGC 2403
ID:
ivo://CDS.VizieR/J/ApJ/853/151
Title:
Oxygen abundances for giant HII regions in NGC 2403
Short Name:
J/ApJ/853/151
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper presents a spectroscopic investigation of 11 HII regions in the nearby galaxy NGC 2403. The HII regions are observed with a long-slit spectrograph mounted on the 2.16m telescope at XingLong station of National Astronomical Observatories of China. For each of the HII regions, spectra are extracted at different nebular radii along the slit-coverage. Oxygen abundances are empirically estimated from the strong-line indices R23, N2O2, O3N2, and N2 for each spectrophotometric unit, with both observation- and model-based calibrations adopted into the derivation. Radial profiles of these diversely estimated abundances are drawn for each nebula. In the results, the oxygen abundances separately estimated with the prescriptions on the basis of observations and models, albeit from the same spectral index, systematically deviate from each other; at the same time, the spectral indices R23 and N2O2 are distributed with flat profiles, whereas N2 and O3N2 exhibit apparent gradients with the nebular radius. Because our study naturally samples various ionization levels, which inherently decline at larger radii within individual HII regions, the radial distributions indicate not only the robustness of R23 and N2O2 against ionization variations but also the sensitivity of N2 and O3N2 to the ionization parameter. The results in this paper provide observational corroboration of the theoretical prediction about the deviation in the empirical abundance diagnostics. Our future work is planned to investigate metal-poor HII regions with measurable Te, in an attempt to recalibrate the strong-line indices and consequently disclose the cause of the discrepancies between the empirical oxygen abundances.