Search

Start Over Subject emission line stars Content Level Research
1. Active deep learning in large spectros. surveys
ID:
ivo://CDS.VizieR/J/A+A/643/A122
Title:
Active deep learning in large spectros. surveys
Short Name:
J/A+A/643/A122
Date:
21 Oct 2021
Publisher:
CDS
Description:
Current archives of the LAMOST telescope contain millions of pipeline-processed spectra that have probably never been seen by human eyes. Most of the rare objects with interesting physical properties, however, can only be identified by visual analysis of their characteristic spectral features. A proper combination of interactive visualisation with modern machine learning techniques opens new ways to discover such objects. We apply active learning classification methods supported by deep convolutional neural networks to automatically identify complex emission-line shapes in multi-million spectra archives. We used the pool-based uncertainty sampling active learning method driven by a custom-designed deep convolutional neural network with 12 layers. The architecture of the network was inspired by VGGNet, AlexNet, and ZFNet, but it was adapted for operating on one-dimensional feature vectors. The unlabelled pool set is represented by 4.1 million spectra from the LAMOST data release 2 survey. The initial training of the network was performed on a labelled set of about 13000 spectra obtained in the 400{AA} wide region around H{alpha} by the 2m Perek telescope of the Ondrejov observatory, which mostly contains spectra of Be and related early-type stars. The differences between the Ondrejov intermediate-resolution and the LAMOST low-resolution spectrographs were compensated for by Gaussian blurring and wavelength conversion. After several iterations, the network was able to successfully identify emission-line stars with an error smaller than 6.5%. Using the technology of the Virtual Observatory to visualise the results, we discovered 1013 spectra of 948 new candidates of emission-line objects in addition to 664 spectra of 549 objects that are listed in SIMBAD and 2644 spectra of 2291 objects identified in an earlier paper of a Chinese group led by Wen Hou. The most interesting objects with unusual spectral properties are discussed in detail.
2. Allsky cross-matched 3XMMe catalogue
ID:
ivo://CDS.VizieR/IX/48
Title:
Allsky cross-matched 3XMMe catalogue
Short Name:
IX/48
Date:
21 Oct 2021
Publisher:
CDS
Description:
ARCHES (Astronomical Resource Cross-matching for High Energy Studies) is a FP7-Space funded project whose aim is to provide the astronomical community with well-characterised multi-wavelength data in the form of spectral energy distributions (SEDs) for large samples of objects extracted from the 3XMM DR5 X-ray catalogue of serendipitous sources. The project has developed new tools implementing fully probabilistic simultaneous cross-correlation of several catalogues for unresolved sources. A cleaned and enhanced version of the 3XMM DR5 catalogue (the 3XMMe catalogue) has been cross-correlated using the ARCHES tool with a number of selected multi-wavelength archival catalogues. These catalogues cover wavelengths ranging from UV to far IR. They provide probabilities of associations, magnitude and fluxes from which spectral energy distributions can be extracted.
3. A search for accreting young companions
ID:
ivo://CDS.VizieR/J/A+A/622/A156
Title:
A search for accreting young companions
Short Name:
J/A+A/622/A156
Date:
21 Oct 2021
Publisher:
CDS
Description:
In recent years, our understanding of giant planet formation progressed substantially. There have even been detections of a few young protoplanet candidates still embedded in the circumstellar disks of their host stars. The exact physics that describes the accretion of material from the circumstellar disk onto the suspected circumplanetary disk and eventually onto the young, forming planet is still an open question. We seek to detect and quantify observables related to accretion processes occurring locally in circumstellar disks, which could be attributed to young forming planets. We focus on objects known to host protoplanet candidates and/or disk structures thought to be the result of interactions with planets. We analyzed observations of six young stars and their surrounding environments with the SPHERE/ZIMPOL instrument on the Very Large Telescope (VLT) in the H{alpha} filter (656nm) and a nearby continuum filter (644.9nm). We redetect the known accreting M-star companion HD142527 B with the highest published signal to noise to date in both H{alpha} and the continuum. No other companions are detected. We analyzed observations of six young stars (age 3.5-10Myr) and their surrounding environments with the SPHERE/ZIMPOL instrument on the Very Large Telescope (VLT) in the H{alpha}filter (656nm) and a nearby continuum filter (644.9nm). We applied several point spread function (PSF) subtraction techniques to reach the highest possible contrast near the primary star, specifically investigating regions where forming companions were claimed or have been suggested based on observed disk morphology.
4. AS 78 & MWC 657 spectroscopy
ID:
ivo://CDS.VizieR/J/A+AS/147/5
Title:
AS 78 & MWC 657 spectroscopy
Short Name:
J/A+AS/147/5
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of low- and high-resolution spectroscopic and multicolour photometric observations of two early-type emission-line stars, AS 78 and MWC 657. They were identified by Dong & Hu (1991ChA&A..15..275D) with the IRAS sources 03549+5602 and 22407+6008, respectively, among many other sources displaying a very strong infrared excess, V-[25]>=8mag. AS 78 is recognized as a photometric variable for the first time. A large near-IR excess radiation is detected in AS 78 and confirmed by new, higher-quality, data for MWC 657. Significant variations in the Balmer line profiles are detected for both objects. Modelling of the Balmer line profiles of AS 78 obtained in 1994 yields the following parameters of the star and its wind: T_eff_~17000K, logL_bol_/L_{sun}_~4.0, dM/dt~10^-6^M_{sun}_/yr. The photometric and new spectroscopic data indicate that the star's T_eff_ increases with time, while the stellar wind changes its structure. Distances towards both objects are estimated on the basis of their radial velocities and the galactic rotation curve. Consideration of different options about the nature and evolutionary state of both objects leads us to suggest that they are binary systems containing a B-type intermediate-luminosity star and a gaseous disk around the less luminous component.
5. A study of dust nucleation in Mira. Part I.
ID:
ivo://CDS.VizieR/J/A+A/592/A42
Title:
A study of dust nucleation in Mira. Part I.
Short Name:
J/A+A/592/A42
Date:
21 Oct 2021
Publisher:
CDS
Description:
Dust is efficiently produced by cool giant stars, but the condensation of inorganic dust is poorly understood. Observations of key aluminum bearing molecules around evolved stars has enabled us to investigate the nucleation of alumina (Al_2_O_3_) dust in the gas. Aims. We aim to identify and characterize aluminum bearing species in the circumstellar gas of Mira (o Ceti) in order to elucidate their role in the production of Al_2_O_3_ dust. We used multiepoch spectral line observations at (sub-)millimeter, far-infrared, and optical wavelengths including: maps with ALMA that probe the gas distribution in the immediate vicinity of the star at ~30mas; observations with ALMA, APEX, and Herschel in 2013-2015 for studying cycle and inter-cycle variability of the rotational lines of Al-bearing molecules; optical records as far back as 1965 to examine variations in electronic transitions over time spans of days to decades; and velocity measurements and excitation analysis of the spectral features that constrain the physical parameters of the gas.
6. Atlas of B6-A2 hyper- and supergiants
ID:
ivo://CDS.VizieR/J/A+A/397/1035
Title:
Atlas of B6-A2 hyper- and supergiants
Short Name:
J/A+A/397/1035
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an atlas of spectra of 5 emission-line stars: the low-luminosity luminous blue variables (LBVs) HD 168625 and HD 160529, the white hypergiants (and LBV candidates) HD 168607 and AS 314, and the supergiant HD 183143. The spectra were obtained with 2 echelle spectrometers at the 6-m telescope of the Russian Academy of Sciences in the spectral range 4800 to 6700{AA}, with a resolution of 0.4{AA}. We have identified 380 spectral lines and diffuse interstellar bands within the spectra. Specific spectral features of the objects are described.
7. Binary central stars of SMC PNe
ID:
ivo://CDS.VizieR/J/A+A/561/A8
Title:
Binary central stars of SMC PNe
Short Name:
J/A+A/561/A8
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Optical Gravitational Lensing Experiment (OGLE), originally designed to search for microlensing events, provides a rich and uniform data set suitable for studying the variability of certain types of objects. We used the OGLE data to study the photometry of central stars of planetary nebulae (PNe) in the Small Magellanic Cloud (SMC). In particular, we searched for close binary central stars with the aim to constrain the binary fraction and period distribution in the SMC. We also searched for PNe mimics and removed them from the PNe sample. We identified 52 counterparts of PNe in the SMC in the I-band images from the OGLE-II and OGLE-III surveys. We analysed the time-series photometry of the PNe. Spectra of the photometric variables were obtained to constrain the nature of the objects or search for additional evidence for binarity. Eight variables were found. Of these, seven objects are PNe mimics, including one symbiotic star candidate. One close binary central star of PN with a period of 1.15 or 2.31 day was discovered. The obtained binary fraction for the SMC PNe and the observational biases are discussed in terms of the OGLE observations.
8. Bright Be shell stars
ID:
ivo://CDS.VizieR/J/A+A/459/137
Title:
Bright Be shell stars
Short Name:
J/A+A/459/137
Date:
21 Oct 2021
Publisher:
CDS
Description:
Echelle observations are presented and discussed for 23 of the 27 known "normal" shell stars brighter than about 6.5mag. In addition to those typical cases, three stars with known transitions between emission & shell and pure emission line appearance, and three rapidly rotating B stars without records of line emission (Bn stars) are added to the sample.
9. BV(RI)_C_JHK H{alpha} photometry in IC 5146
ID:
ivo://CDS.VizieR/J/AJ/123/304
Title:
BV(RI)_C_JHK H{alpha} photometry in IC 5146
Short Name:
J/AJ/123/304
Date:
21 Oct 2021
Publisher:
CDS
Description:
The B0V star BD+46 3474 lies near the front surface of a dense molecular cloud and illuminates the emission/reflection nebula IC 5146. The HAeBe variable BD +46 3471 is embedded in the same cloud, about 10' (3.5pc) away. CCD photometry in BV(RI)_C_ (to V=22) and in JHK (to about K=16.5) has been obtained for the young clusters surrounding each of these two bright stars. Some 100 emission-H{alpha} stars brighter than R=20.5 have been found in the area, most of them in IC 5146. (Among these are two that have spectra resembling a high-excitation Herbig-Haro [HH] object plus a stellar continuum).
10. BV(RI)c photometry of 7 symbiotic stars
ID:
ivo://CDS.VizieR/J/A+A/370/503
Title:
BV(RI)c photometry of 7 symbiotic stars
Short Name:
J/A+A/370/503
Date:
21 Oct 2021
Publisher:
CDS
Description:
File table1.dat contains the UBV(RI)c magnitudes of the symbiotic stars AS 323, Ap 3-1, CM Aql, V1413 Aql, V443 Her, V627 Cas, V919 Sgr estimated on the Asiago archive plates. The date is given in the year/month/day format, and the magnitude is estimated in steps of 0.05mag

Limit your search

more »

  • 2116