- ID:
- ivo://CDS.VizieR/J/A+A/563/L10
- Title:
- BD+33 2642 and HD 112313 radial velocities
- Short Name:
- J/A+A/563/L10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the impact of binary interaction processes on the evolution of low- and intermediate-mass stars using long-term monitoring of their radial velocity. Here we report on our results on the central stars of two planetary nebulae (PNe): the well-studied spectrophotometric standard BD+33 2642 (central star of PNG 052.7+50.7) and HD 112313 (central star of PN LoTr5), the optical light of which is dominated by a rapidly rotating G star.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/752/56
- Title:
- BDKP. III. Parallaxes for 70 ultracool dwarfs
- Short Name:
- J/ApJ/752/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report parallax measurements for 70 ultracool dwarfs (UCDs) including 11 late-M, 32 L, and 27 T dwarfs. In this sample, 14 M and L dwarfs exhibit low surface gravity features, 6 are close binary systems, and 2 are metal-poor subdwarfs. We combined our new measurements with 114 previously published UCD parallaxes and optical-mid-IR photometry to examine trends in spectral-type/absolute magnitude, and color-color diagrams. We report new polynomial relations between spectral type and M_JHK_. Including resolved L/T transition binaries in the relations, we find no reason to differentiate between a "bright" (unresolved binary) and a "faint" (single source) sample across the L/T boundary. Isolating early T dwarfs, we find that the brightening of T0-T4 sources is prominent in M_J_ where there is a [1.2-1.4] mag difference. A similar yet dampened brightening of [0.3-0.5] mag happens at M_H_ and a plateau or dimming of [-0.2 to -0.3] mag is seen in M_K_. Comparison with evolutionary models that vary gravity, metallicity, and cloud thickness verifies that for L into T dwarfs, decreasing cloud thickness reproduces brown dwarf near-IR color-magnitude diagrams. However we find that a near constant temperature of 1200 +/-100 K along a narrow spectral subtype of T0-T4 is required to account for the brightening and color-magnitude diagram of the L-dwarf/T-dwarf transition. There is a significant population of both L and T dwarfs which are red or potentially "ultra-cloudy" compared to the models, many of which are known to be young indicating a correlation between enhanced photospheric dust and youth. For the low surface gravity or young companion L dwarfs we find that 8 out of 10 are at least [0.2-1.0] mag underluminous in M_JH_and/or M_K_compared to equivalent spectral type objects. We speculate that this is a consequence of increased dust opacity and conclude that low surface gravity L dwarfs require a completely new spectral-type/absolute magnitude polynomial for analysis.
- ID:
- ivo://CDS.VizieR/J/ApJS/220/18
- Title:
- BDKP IV. RVs of late-M and L dwarfs with MagE
- Short Name:
- J/ApJS/220/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radial velocity measurements are presented for 85 late M- and L-type very low-mass stars and brown dwarfs obtained with the Magellan Echellette spectrograph. Targets primarily have distances within 20pc of the Sun, with more distant sources selected for their unusual spectral energy distributions. We achieved precisions of 2-3km/s, and combined these with astrometric and spectrophotometric data to calculate UVW velocities. Most are members of the thin disk of the Galaxy, and velocity dispersions indicate a mean age of 5.2+/-0.2Gyr for sources within 20pc. We find significantly different kinematic ages between late-M dwarfs (4.0+/-0.2Gyr) and L dwarfs (6.5+/-0.4Gyr) in our sample that are contrary to predictions from prior simulations. This difference appears to be driven by a dispersed population of unusually blue L dwarfs which may be more prevalent in our local volume-limited sample than in deeper magnitude-limited surveys. The L dwarfs exhibit an asymmetric U velocity distribution with a net inward flow, similar to gradients recently detected in local stellar samples. Simulations incorporating brown dwarf evolution and Galactic orbital dynamics are unable to reproduce the velocity asymmetry, suggesting non-axisymmetric perturbations or two distinct L dwarf populations. We also find the L dwarfs to have a kinematic age-activity correlation similar to more massive stars. We identify several sources with low surface gravities, and two new substellar candidate members of nearby young moving groups: the astrometric binary DENIS J08230313-4912012AB, a low-probability member of the {beta} Pictoris Moving Group; and 2MASS J15104786-2818174, a moderate-probability member of the 30-50Myr Argus Association.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A60
- Title:
- BD+46 442 optical spectra
- Short Name:
- J/A+A/607/A60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim at describing and understanding binary interaction processes in systems with very evolved companions. Here, we focus on understanding the origin and determining the properties of the high-velocity outflow observed in one such system. We present a quantitative analysis of BD+46 442, a post-AGB binary which shows active mass transfer that leads to the creation of a disk-driven outflow or jet. We obtained high-resolution optical spectra from the HERMES spectrograph, mounted on the 1.2m Flemish Mercator Telescope. By performing a time-series analysis of the H{alpha} profile, we dissected the different components of the system. We deduced the jet geometry by comparing the orbital phased data with our jet model. In order to image the accretion disk around the companion of BD+46 442, we applied the technique of Doppler tomography. Results: The orbital phase-dependent variations in the H{alpha} profile can be related to an accretion disk around the companion, from which a high-velocity outflow or jet is launched. Our model shows that there is a clear correlation between the inclination angle and the jet opening angle. The latitudinally dependent velocity structure of our jet model shows a good correspondence to the data, with outflow velocities at least higher than 400km/s. The intensity peak in the Doppler map might be partly caused by a hot spot in the disk, or a larger asymmetrical structure in the disk. We show that BD+46 442, is a result of a binary interaction channel. The origin of the fast outflow in this system can be attributed to a gaseous disk around the secondary component, which is most likely a main sequence star. Our analysis suggests the outflow to have a rather wide opening angle instead of being strongly collimated. Our time resolved spectral monitoring reveals the launching site of the jet in the binary BD+46 442. Similar orbital phase-dependent H{alpha} profiles are commonly observed in post-AGB binaries. Post-AGB binaries provide ideal test bets to study jet formation and launching mechanisms over a wide range of orbital conditions.
- ID:
- ivo://CDS.VizieR/J/A+A/576/A66
- Title:
- BD+20 1790 radial velocities and photometry
- Short Name:
- J/A+A/576/A66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In a previous paper we reported a planetary companion to the young and very active K5Ve star BD+20 1790. This paper aims to more rigorously assess the nature of the radial velocity measurements with an expanded data set and new methods of analysis. We have employed Bayesian methods to simultaneously analyse the radial velocity and activity measurements based on a combined data set that includes new and previously published observations.
- ID:
- ivo://CDS.VizieR/J/A+A/513/L8
- Title:
- BD+20 1790 radial velocity curve
- Short Name:
- J/A+A/513/L8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The young active star BD +20 1790 has been inferred to host a substellar companion from radial-velocity measurements that detected the reflex motion induced on the parent star. We attempt to completely characterize the radial-velocity signal in order to assess its nature.
- ID:
- ivo://CDS.VizieR/J/A+A/319/593
- Title:
- [Be] abundances in low-metallicity stars
- Short Name:
- J/A+A/319/593
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present observations of the Be II 313.0nm resonance doublet in 14 halo and old disk stars with metallicities ranging from [Fe/H]=-0.4 to =~-3.0 obtained with the CASPEC spectrograph of the ESO 3.6m telescope at a FWHM=~8.6km/s resolution. Abundances are derived by means of the synthetic spectra technique employing Kurucz (1993, CD-ROM 13 and CD-ROM 18) atmospheric models, with enhanced {alpha}-elements and no overshooting.
- ID:
- ivo://CDS.VizieR/J/PASP/132/K4102
- Title:
- Beamed and unbeamed emission of gamma-ray blazars
- Short Name:
- J/PASP/132/K4102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A two-component model of radio emission has been used to explain some radio observational properties of Active Galactic Nuclei (AGNs) and, in particular, of blazars. In this work, we extend the two-component idea to the {gamma}-ray emission and assume that the total {gamma}-ray output of blazars consists of relativistically beamed and unbeamed components. The basic idea leverages the correlation between the radio core-dominance parameter and the {gamma}-ray beaming factor. To do so, we evaluate this correlation for a large sample of 584 blazars taken from the fourth source catalog of the Fermi Large Area Telescope (Fermi-LAT) and correlated their {gamma}-ray core-dominance parameters with radio core-dominance parameters. The {gamma}-ray beaming factor is then used to estimate the beamed and unbeamed components. Our analysis confirms that the {gamma}-ray emission in blazars is mainly from the beamed component.
- ID:
- ivo://CDS.VizieR/J/ApJ/645/856
- Title:
- Beamed radio-intermediate quasars
- Short Name:
- J/ApJ/645/856
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Whether radio-intermediate quasars possess relativistic jets as radio-loud quasars do is an important issue in the understanding of the origin of radio emission in quasars. In this paper, using the two-epoch radio data obtained during the Faint Images of the Radio Sky at Twenty cm (FIRST) and NRAO VLA Sky Survey (NVSS), we identified 89 radio-variable sources in the Sloan Digital Sky Survey (SDSS). Among them, more than half are radio-intermediate quasars (RL=f_20cm_/f_2500{AA}_<250). For all objects with available multiple-band radio observations, the radio spectra are either flat or inverted. The brightness temperature inferred from the variability is larger than the synchrotron self-Compton limit for a stationary source in 87 objects, indicating relativistic beaming. Considering the sample selection and the viewing angle effect, we conclude that relativistic jets probably exist in a substantial fraction of radio-intermediate quasars.
- ID:
- ivo://CDS.VizieR/J/A+A/634/A18
- Title:
- Be and Bn stars Balmer discontinuity
- Short Name:
- J/A+A/634/A18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A significant number of Be stars show a second Balmer discontinuity (sBD) attributed to an extended circumstellar envelope (CE). The fast rotational velocity of Be stars undoubtedly plays a significant role in the formation of the CE. However, Bn stars, which are also B-type rapidly rotating stars, do not all present clear evidence of being surrounded by circumstellar material. We aim to characterize the populations of Be and Bn stars, and discuss the appearance of the sBD as a function of the stellar parameters. We expect to find new indices characterizing the properties of CEs in Be stars and properties relating Be and Bn stars. We obtained low- and high-resolution spectra of a sample of Be and Bn stars, derived stellar parameters, characterized the sBD, and measured the emission in the H{alpha} line. Results. Correlations of the aspect and intensity of the sBD and the emission in the H{alpha} line with the stellar parameters and the Vsini are presented. Some Bn stars exhibit the sBD in absorption, which may indicate the presence of rather dense CEs. Six Bn stars show emission in the H{alpha} line, so they are reclassified as Be stars. The sBD in emission appears in Be stars with Vsini<=250km/s, and in absorption in both Be and Bn stars with Vsini>=50km/s Low-mass Be and Bn stars share the same region in the Hertzsprung-Russell diagram. The distributions of rotational to critical velocity ratios of Be and Bn stars corresponding to the current stellar evolutionary stage are similar, while distributions inferred for the zero-age main sequence have different skewness. We found emission in the H{alpha} line and signs of a CE in some Bn stars, which motivated us to think that Bn and Be stars probably belong to the same population. It should be noted that some of the most massive Bn stars could display the Be phenomenon at any time. The similarities found among Be and Bn stars deserve to be more deeply pursued.
