Emission Stars Research Articles

Finding The Relationship between Pulsation Motion and Hα Emission Lines on γ Cas using Photometric and Spectroscopic Data

Abstract Pulsating stars show variability in brightness due to changes in their volume. There are two types of pulsation/oscillation: radial and non-radial. Radial oscillation keeps the symmetrical shape of the star, while non-radial oscillation does not. We study a pulsating star: γ Cas, classified as a B0.5 IVe variable star because of its pulsations and also an emission star due to the emission lines in its spectra. When a star pulsates, its atmosphere expands and contracts, potentially leading to the formation of shock waves. Observational features such as discontinuities in the radial velocity curve and emission lines support this phenomenon. In this study, we analyse the relationship between pulsation motion and the H α emission lines of γ Cas using photometric and spectroscopic data. Photometric data is obtained from the BRIght Target Explorer (BRITE) catalog, while spectroscopic data comes from the Be Star Spectra (BeSS) catalog. Both datasets cover the same observational dates: August 28 to October 26, 2015. Confirming the pulsation period of γ Cas at 1.21 days, we also discover an added pulsation period of 10 days from photometric data. To confirm this, we examine spectroscopic data from three specific dates: August 28, September 7, and 27, 2015. Notably, the relative flux of the H α emission lines continue to increase, leading us to conclude that these lines are indeed caused by the pulsation of γ Cas.

The Discovery of Three Galactic Wolf–Rayet Stars

Wolf–Rayet stars (WRs) are evolved massive stars in the brief stage before they undergo core collapse. Not only are they rare, but they also can be particularly difficult to find due to the high extinction in the Galactic plane. This paper discusses the discovery of three new Galactic WRs previously classified as Hα emission stars, but thanks to Gaia spectra, we were able to identify the broad, strong emission lines that characterize WRs. Using the Lowell Discovery Telescope and the DeVeny spectrograph, we obtained spectra for each star. Two are WC9s, and the third is a WN6 + O6.5 V binary. The latter is a known eclipsing system with a 4.4 day period from ASAS-SN data. We calculate absolute visual magnitudes for all three stars to be between −7 and −6, which is consistent with our expectations of these subtypes. These discoveries highlight the incompleteness of the WR census in our local volume of the Milky Way and suggest the potential for future Galactic WR discoveries from Gaia low-dispersion spectra. Furthermore, radial velocity studies of the newly found binary will provide direct mass estimates and orbital parameters, adding to our knowledge of the role that binarity plays in massive star evolution.

Analysis of Gaia DR3 Data of Selected High Galactic Latitude Hα Emission Stars

Gaia DR3 data of 52 high galactic latitude Hα emission stars selected from the paper of Stephenson are analyzed. Ten new variable stars and eight new high velocity stars have been found. Details of six post-AGB stars and several other interesting stars are discussed. Many of the stars presented in this paper have Gaia DR3 light curves and spectra. A detailed study of these 52 stars is needed to derive their chemical composition and to further understand their binarity, circumstellar matter and evolutionary status. The astrophysical parameters from the Gaia DR3 data reveal several hot (OBA) and several F and G-type stars in this sample. Some of them are metal-poor stars.

A low-mass hub–filament with double centre revealed in NGC 2071-North

ABSTRACT We present the first analysis in NGC 2071-North as a resolved hub–filament featuring a double centre. This ∼1.5 × 1.5 pc2 scale filament hub contains ∼500 M⊙. Seen from Planck, magnetic field lines may have facilitated the gathering of material at this isolated location. The energy balance analysis, supported by infalling gas signatures, reveals that these filaments are currently forming stars. Herschel 100 $\mu$m emission concentrates in the hub, at IRAS 05451+0037 and LkHα 316, and presents diffuse lobes and loops around them. We suggest that such a double centre could be formed, because the converging locations of filament pairs are offset, by 2.3 arcmin (0.27 pc). This distance also matches the diameter of a hub ring, seen in column density and molecular tracers, such as HCO+ (1–0) and HCN (1–0), that may indicate a transition and the connection between the hub and the radiating filaments. We argue that all of the three components of the emission star LkHα 316 are in physical association. We find that a ∼0.06-pc-sized gas loop, attached to IRAS 05451+0037, can be seen at wavelengths all the way from the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS)-i to Herschel 100 $\mu$m. These observations suggest that both protostars at the double hub centre are interacting with the cloud material. In our 13CO data, we do not seem to find the outflow of this region that was identified in the 1980s with much lower resolution.

A Search for T Tauri Stars toward Nearby, Dense Cores

We have searched 14 dense cores, 11 of which have literature distances of 150–350 pc, for T Tauri stars by using the Wide Field Grism Spectrograph 2 on the University of Hawaii 2.2 m telescope. As a result, we detected 50 Hα emission stars including 24 newly found objects. Twelve out of these 50 stars have a distance of ∼190–370 pc, and 16 of them are within a distance of ∼460 pc. Seven of these 16 objects are newly found Hα emission stars and would serve as new good targets for studying protoplanetary disks and young exoplanets.

WIYN Open Cluster Study. LXXXIV. The Effect of Chromospheric Activity on Oxygen Abundances from the 7774 Å Triplet in Pleiades Dwarfs

Abstract We present a spectroscopic analysis of 7774 Å O i triplet abundances, 8498–8662 Å Ca ii triplet chromospheric activity, and rotation in the Pleiades open cluster, with the objective of thoroughly examining the O triplet overabundance trends observed in cool open cluster dwarfs, and to thereby make clear the cause of that trend. High-dispersion, contemporaneous spectra of the O i triplet, Ca ii triplet, and Hα spectral regions in 41 Pleiades dwarfs were acquired using Hydra on the WIYN 3.5 m telescope. Our Ca ii emission equivalent-width data exhibit a strong positive correlation with decreasing T eff, with the rapidly rotating stars enhanced by up to 50% above the slowly rotating stars. Our triplet [O/H] values exhibit a statistically significant positive correlation with total Ca ii triplet emission, and similarly, significant correlations have been found by every study to date that used contemporaneous O triplet abundance and chromospheric activity data, which is strong evidence that chromospheric activity is the cause of the observed overabundance trends. Based on the slowly rotating, low Ca ii emission stars in the near-solar range 5450 K < T eff < 6100 K, we find a cluster mean [O/H] = + 0.143 ± 0.061, consistent with the substantial super-solar [O/H] values exhibited by most young ( < 1 Gyr) open clusters. We also find a cluster mean [Fe/H] = + 0.029 ± 0.034, in excellent agreement with previous studies.

Spectral Observations of Emission Stars in the Vicinity of Cyg OB7

Results from spectral observations of known emission stars in the vicinity of Cyg OB7 are presented. 64 spectra of 9 emission stars were obtained over the period 2001-2007. The equivalent widths of the most characteristic lines for T-Tau stars were obtained in all these spectra. It is noted that all the spectral lines manifest strong variations. The spectra of these stars are in the spectral range K8-M4. Two stars (Nos. 12 and 23) have a negative Balmer jump. The forbidden [OIII] 4959 and 5007 A and [SII] 6716/31 A lines, which are typical of classical T-Tau stars, show up in the spectra of stars No. 23 and 86.

Hα emission-line stars in molecular clouds

A deep objective-prism survey for Hα emission stars towards the Canis Major star-forming clouds was performed. A total of 398 Hα emitters were detected, 353 of which are new detections. There is a strong concentration of these Hα emitters towards the molecular clouds surrounding the CMa OB1 association, and it is likely that these stars are young stellar objects recently born in the clouds. An additional population of Hα emitters is scattered all across the region, and probably includes unrelated foreground dMe stars and background Be stars. About 90% of the Hα emitters are detected by WISE, of which 75% was detected with usable photometry. When plotted in a WISE colour–colour diagram it appears that the majority are Class II YSOs. Coordinates and finding charts are provided for all the new stars, and coordinates for all the detections. We searched the Gaia-DR2 catalogue and from 334 Hα emission stars with useful parallaxes, we selected a subset of 98 stars that have parallax errors of less than 20% and nominal distances in the interval 1050 to 1350 pc that surrounds a strong peak at 1185 pc in the distance distribution. Similarly, Gaia distances were obtained for 51 OB-stars located towards Canis Major and selected with the same parallax errors as the Hα stars. We find a median distance for the OB stars of 1182 pc, in excellent correspondence with the distance from the Hα stars. Two known runaway stars are confirmed as members of the association. Finally, two new Herbig-Haro objects are identified.

Investigating the origin of the spectral line profiles of the Hot Wolf–Rayet Star WR 2

The hot WN star WR2 (HD6327) has been claimed to have many singular characteristics. To explain its unusually rounded and relatively weak emission line profiles, it has been proposed that WR2 is rotating close to break-up with a magnetically confined wind. Alternatively, the line profiles could be explained by the dilution of WR2's spectrum by that of a companion. In this paper, we present a study of WR2 using near-infrared AO imaging and optical spectroscopy and polarimetry. Our spectra reveal the presence of weak photospheric absorption lines from a ~B2.5-4V companion, which however contributes only ~5-10% to the total light, suggesting that the companion is a background object. Therefore, its flux cannot be causing any significant dilution of the WR star's emission lines. The absence of intrinsic linear continuum polarization from WR2 does not support the proposed fast rotation. Our Stokes V spectrum was not of sufficient quality to test the presence of a moderately strong organized magnetic field but our new modelling indicates that to confine the wind the putative magnetic field must be significantly stronger than was previously suggested sufficiently strong as to make its presence implausible.

Frequency Analysis of a Potential SPB Star η Tau

In this study, five years of photometric data of η Tau obtained from the STEREO satellite between 2007 and 2011 are presented. The high-precision data are compared with the results derived from the spectroscopic findings to gain a better understanding of the Be phenomenon in the star. The spectroscopic data cover the same time interval as the photometric observations. η Tau displays a double peaked Hα emission profile in its spectra. In order to analyze this profile, the Hα emission lines are examined by measuring their equivalent widths and line intensities. As a result of the photometric and spectroscopic analyses, it is revealed that the frequency distribution and amplitude intensities of the star are different from those of a typical Be star. Based on its physical parameters such as temperature and luminosity values, it may be conclude that the star is a Slowly Pulsating B type emission star. On the other hand, the equivalent width values of the emission lines appear to be related to the oscillation frequencies and their amplitudes. This indicates that the photometric variations may be related to the environmental disc structure.Doğuş ÖZUYAR, dozuyar@ankara.edu.tr, ORCID: https://orcid.org/ 0000-0001-8544-0950

Some important notes on ASTA software: A new method of analysis of simple and complex emission and absorption spectral lines

Abstract ASTA is a new spectral analysis software aiming to serve the growing need of an integrated computing environment which will implement efficiently the demanding process of multicomponent analysis. It is a cutting-edge spectral multicomponent analysis software for displaying, fitting and analyzing astronomical spectra of complex emission and absorption line profiles. Equipped with statistical and verification tools it accelerates complex mathematical precision checks and confirms the uniqueness of the calculated physical parameters and the number of the absorption components that construct every Broad Absorption/Emission Line (BAL/BEL) and Discrete Absorption Components (DACs). DACs (in the case of Hot Emission Stars) and BALs/BELs (in the case of Quasars) are spectral lines of the same ion and the same wavelength as the main spectral line, shifted at different Δ λ , as they are created in different density regions which rotate and move radially with different velocities. The currently accepted view is that BELs, BALs and DACs may be due to a flow of many individual density enhancements, called clouds, cloudlets or clumps which are optically thick and very small compared with the size of the central continuum source. These density enhancements are not preexisting entities but are formed inside an unstable and turbulent wind and they are indicated by very complex profiles. According to this phenomenon, a prevailing view is that they are not simple absorption/emission lines, but the synthesis of a group of classical absorption line components of the same spectral line. ASTA software equipped with a multicomponent analysis model is a novel approach to curve fit these complex lines focusing on the physical representation of the calculated parameters of each of these components. The BAL Quasar SDSS J114548.38 + 393746.6 case study is analyzed to demonstrate the potential of ASTA, whereas the Quasar SDSS 27.01 + 030715.5 narrow absorption line highlights the flexibility to analyze effectively simple spectral profiles.

An Automated Tool to Detect Variable Sources in the Vista Variables in the Vía Láctea Survey: The VVV Variables (V4) Catalog of Tiles d001 and d002

AbstractTime-varying phenomena are one of the most substantial sources of astrophysical information, and their study has led to many fundamental discoveries in modern astronomy. We have developed an automated tool to search for and analyze variable sources in the near-infraredKsband using the data from the VISTA Variables in the Vía Láctea (VVV) ESO Public Large Survey. This process relies on the characterization of variable sources using different variability indices calculated from time series generated with point-spread function (PSF) photometry of sources under analysis. In particular, we used two main indices, the total amplitudeand the eta indexη, to identify variable sources. Once the variable objects are identified, periods are determined with generalized Lomb–Scargle periodograms and the information potential metric. Variability classes are assigned according to a compromise between comparisons with VVV templates and the period of the variability. The automated tool is applied on VVV tiles d001 and d002 and led to the discovery of 200 variable sources. We detected 70 irregular variable sources and 130 periodic ones. In addition, nine open-cluster candidates projected in the region are analyzed, and the infrared variable candidates found around these clusters are further scrutinized by cross-matching their locations against emission star candidates from VPHAS+ survey Hαcolor cuts.

On the evolutionary state of massive stars in transition phases in M33

The advanced stages of several high-mass stars are characterized by episodic mass loss shed during phases of instability. Key for assigning these stars a proper evolutionary state is to assess the composition and geometry of their ejecta alongside the stellar properties. We selected five hot LBV candidates in M33 to refine their classification, investigate their circumstellar environments and explore their evolutionary properties. Being accessible targets in the near-infrared, we conducted medium-resolution spectroscopy with GNIRS/GEMINI in the $K-$band to investigate their molecular circumstellar environments. Two stars were found to display CO emission, which was modeled to emerge from a circumstellar or circumbinary Keplerian disk/ring. The identification of the carbon isotope $^{13}$C and, for one of the two stars, a significantly low $^{12}$CO/$^{13}$CO ratio, implies an evolved stellar state. As both CO emission stars are highly luminous and hence do not undergo a red supergiant phase, we suggest that stripping processes and equatorial high-density ejecta due to fast rotation are responsible for the enrichment of the stellar surface with processed material from the core. A candidate B[e]SG displays an absorption CO profile, which may be attributed to a jet or stellar pulsations. The featureless infrared spectra of two stars suggest a low-density gas shell or dissipation of the molecule due to the ionizing temperature of the star. We propose spectroscopic monitoring of our targets to evaluate the stability of the CO molecule and assess the time-dependent dynamics of the circumstellar gas structures.

The Multiple Pre-main-sequence System PR Ori and the Associated HH 305 Flow

Abstract A detailed imaging and spectroscopic analysis is presented of the little-studied T Tauri star PR Ori and its associated Herbig–Haro flow HH 305, located on the outskirts of the L1641-N cluster in Orion. PR Ori is shown to be a multiple system, where the A component is a close 0.″077 binary, and the B component, at a distance of 3.″50, is the driver of the large Herbig–Haro flow. A low-luminosity source, here called C, is located 9.″3 to the southeast and is shown spectroscopically to be straddling the stellar/brown dwarf boundary. The corresponding separations in projection are 32, 1450, and 3900 au, respectively. Although PR Ori A is a weak-line T Tauri star, high-resolution optical spectra reveal high-velocity outflowing winds and, at the same time, material infalling with speeds up to 200 km s−1. PR Ori B shows a similar combination of outflow and infall but is a strong Hα emission star, with a major near-infrared excess that dominates the luminosity of the system at wavelengths longer than ∼5 μm. HH 305 displays three pairs of knots symmetrically on either side of PR Ori, with higher velocities near the source and gradually decreasing velocities with increasing distance from the source. The innermost knots show bubble-like morphologies, very different from a collimated jet, with the northern lobe redshifted and the southern lobe blueshifted. The origin and nature of this unusual Herbig–Haro flow is discussed.

The star formation environment of the FU Ori type star V582 Aur

We have studied the environment of the FU Ori type star V582 Aur. Our aim is to explore the star-forming region associated with this young eruptive star. Using slitless spectroscopy we searched for H alpha emission stars within a field of 11.5arcmin \times 11.5arcmin, centred on V582 Aur. Based on UKIDSS and Spitzer Space Telescope data we further selected infrared-excess young stellar object candidates. In all, we identified 68 candidate low-mass young stars, 16 of which exhibited H alpha emission in the slitless spectroscopic images. The colour-magnitude diagram of the selected objects, based on IPHAS data, suggests that they are low-mass pre-main-sequence stars associated with the Aur OB 1 association, located at a distance of 1.3 kpc from the Sun. The bright-rimmed globules in the local environment of V582 Aur probably belong to the dark cloud LDN~1516. Our results suggest that star formation in these globules might have been triggered by the radiation field of a few hot members of Aur OB 1. The bolometric luminosity of V582 Aur, based on archival photometric data and on the adopted distance, is 150-320 Lsun.

New Emission Stars in B Cyg OB7

This is a continuation of a search for and study of emission objects in known dark clouds and star formation regions. New results are presented from a search for emission stars in the region of Cyg OB7 where 36 new emission stars have been discovered previously. The current observations were made adjacent to previously studied regions in the vicinity of the object HH 448. 26 new emission stars were found in three small regions with a combined area of 0.11 sq. deg. On an (H-K)-(J-H) two-color diagram these stars lie among the classical T Tau stars (CTTS) and T Tau stars with weak lines (WTTS). A strong change in brightness was recorded for one of the emission stars.

An aggregation-induced emission star polymer with pH and metal ion responsive fluorescence

A one-pot strategy from ring-opening metathesis polymerization was employed to prepare AIE-active star polymers, which were designed to have multi-responsive fluorescence to varied stimuli including pH, CO2, and metal ions.

Statistical Analysis of Stars with Hα Emission in the Cluster IC 348

In this work the results of the statistical analysis of the 215 stars with Ha emission in the IC 348 cluster are presented. The sample is completed to R<20.0.The optical radius is about 11 arcmin. The percentage of emission stars increase from bright to fainter objects and to the range of 13.0<R-AR<19.0 reaches 80%. The ratio between WTTau and CCTau objects is 64% and 36%. The 70% of X-ray sources are WTTau stars. The age of WTTau and CTTau objects are about 2*106 years. The age of the non emission stars with a mass less solar is about 2*106 years also, but non emission more massive objects are "older", the age of them is about 7*106 years. The most massive stars with a low level of activity is concentrated in a small dense central core of the cluster with a radius about 1 arcmin, and apparently, they are generated during an earlier wave of star formation in the cluster.

TheGaia-ESO Survey: Catalogue of Hαemission stars

We discuss the properties of H$\alpha$ emission stars across the sample of 22035 spectra from the Gaia-ESO Survey internal data release, observed with the GIRAFFE instrument and largely belonging to stars in young open clusters. Automated fits using two independent Gaussian profiles and a third component that accounts for the nebular emission allow us to discern distinct morphological types of H$\alpha$ line profiles with the introduction of a simplified classification scheme. All in all we find 3765 stars with intrinsic emission and sort their spectra into eight distinct morphological categories: single--component emission, emission blend, sharp emission peaks, double emission, P-Cygni, inverted P-Cygni, self--absorption, and emission in absorption. We have more than one observation for 1430 stars in our sample, thus allowing a quantitative discussion of the degree of variability of H$\alpha$ emission profiles, which is expected for young, active objects. We present a catalogue of stars with properties of their H$\alpha$ emission line profiles, morphological classification, analysis of variability with time and the supplementary information from the SIMBAD, VizieR, and ADS databases. The records in SIMBAD indicate the presence of H$\alpha$ emission for roughly 25% of all stars in our catalogue, while at least 305 of them have already been more thoroughly investigated according to the references in ADS. The most frequently identified morphological categories in our sample of spectra are emission blend (23%), emission in absorption (22%), and self--absorption (16%). Objects with repeated observations demonstrate that our classification into discrete categories is generally stable through time, but categories P-Cygni and self--absorption seem less stable, which is the consequence of discrete classification rules, as well as of the fundamental change in profile shape.

Efficient Selection and Classification of Infrared Excess Emission Stars Based on AKARI and 2MASS Data

AbstractThe selection of young stellar objects (YSOs) based on excess emission in the infrared is easily contaminated by post-main-sequence stars and various types of emission line stars with similar properties. We define in this paper stringent criteria for an efficient selection and classification of stellar sources with infrared excess emission based on combined Two Micron All Sky Survey (2MASS) and AKARI colors.