- ID:
- ivo://CDS.VizieR/J/MNRAS/432/3186
- Title:
- Symbiotic stars towards the Galactic bulge
- Short Name:
- J/MNRAS/432/3186
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Symbiotic stars are interacting binaries with the longest orbital periods, and their multicomponent structure makes them rich astrophysical laboratories. The accretion of a high-mass-loss-rate red giant wind on to a white dwarf (WD) makes them promising Type Ia supernova (SN Ia) progenitors. Systematic surveys for new Galactic symbiotic stars are critical to identify new promising SN Ia progenitors (e.g. RS Oph) and to better estimate the total population size to compare against SN Ia rates. Central to the latter objective is building a complete census of symbiotic stars towards the Galactic bulge. Here we report on the results of a systematic survey of H{alpha} emission-line stars covering 35 deg^2^. It is distinguished by the combination of deep optical spectroscopy and long-term light curves that improve the certainty of our classifications. A total of 20 bona fide symbiotic stars are found (13 S-types, 6 D-types and 1 D'-type), 35 per cent of which show the symbiotic specific Raman-scattered Ovi emission bands, as well as 15 possible symbiotic stars that require further study (six S-types and nine D-types). Light curves show a diverse range of variability including stellar pulsations (semi-regular and Mira), orbital variations and slow changes due to dust. Orbital periods are determined for five S-types and Mira pulsation periods for three D-types. The most significant D-type found is H1-45 and its carbon Mira with a pulsation period of 408.6d, corresponding to an estimated period-luminosity relation distance of ~6.2+/-1.4kpc and M_K_=-8.06+/-0.12mag. If H1-45 belongs to the Galactic bulge, then it would be the first bona fide luminous carbon star to be identified in the Galactic bulge population. The lack of luminous carbon stars in the bulge is a longstanding unsolved problem. A possible explanation for H1-45 may be that the carbon enhancement was accreted from the progenitor of the WD companion. A wide variety of unusual emission-line stars were also identified. These include central stars of planetary nebulae (PNe) [one (WC10-11) Wolf-Rayet and five with high-density cores], two novae, two WN6 Wolf-Rayet stars, two possible Be stars, a B[e] star with a bipolar outflow, an ultracompact HII region and a dMe flare star. Dust obscuration events were found in two central stars of PNe, increasing the known cases to five, as well as one WN6 star. There is considerable scope to uncover several more symbiotic stars towards the bulge, many of which are currently misclassified as PNe, provided that deep spectroscopy is combined with optical and near-infrared light curves.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+AS/143/343
- Title:
- Symbiotic stars UBV(RI)c photometry
- Short Name:
- J/A+AS/143/343
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present accurate UBV(RI)_C_ photometric sequences around 20 symbiotic stars. The sequences extend over wide brightness and color ranges, and are suited to cover quiescence as well as outburst phases. The sequences are intended to assist both present time photometry as well as measurement of photographic plates from historical archives.
- ID:
- ivo://CDS.VizieR/J/A+A/372/145
- Title:
- Symbiotic stars UBV(RI)c photometry. II.
- Short Name:
- J/A+A/372/145
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present accurate UBV(RI)_C_ photometric sequences for an additional 20 symbiotic stars. As for the 20 targets of Paper I (Henden et al., 2000, Cat. <J/A+AS/143/343>), the sequences extend over wide brightness and color ranges, and are suited to cover both quiescence and outburst phases. The sequences are intended to assist both present time photometry as well as measurement of photographic plates from historical archives.
- ID:
- ivo://CDS.VizieR/J/A+A/458/339
- Title:
- Symbiotic stars UBV(RI)c photometry. III.
- Short Name:
- J/A+A/458/339
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present accurate UBV(RI)_C_ photometric sequences and astrometric positions for a final set of 41 symbiotic stars. In a similar manner to the 40 targets of Papers I and II, these sequences extend over wide brightness and color ranges and are suited to covering both quiescence and outburst phases. They are intended to assist both the CCD photometric monitoring of current variability and exploitation of old photographic plates from historical archives.
- ID:
- ivo://CDS.VizieR/J/ApJS/240/21
- Title:
- Symbiotic stars with 2MASS, WISE & Gaia data
- Short Name:
- J/ApJS/240/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new census of Galactic and extragalactic symbiotic stars (SySts). This compilation contains 323 known and 87 candidate SySts. Of the confirmed SySts, 257 are Galactic and 66 extragalactic. The spectral energy distributions (SEDs) of 348 sources have been constructed using 2MASS and AllWISE data. Regarding the Galactic SySts, 74% are S types, 13% D, and 3.5% D'. S types show an SED peak between 0.8 and 1.7{mu}m, whereas D types show a peak at longer wavelengths between 2 and 4{mu}m. D' types, on the other hand, display a nearly flat profile. Gaia distances and effective temperatures are also presented. According to their Gaia distances, S types are found to be members of both thin and thick Galactic disk populations, while S+IR and D types are mainly thin disk sources. Gaia temperatures show a reasonable agreement with the temperatures derived from SEDs within their uncertainties. A new census of the OVI{lambda}6830 Raman-scattered line in SySts is also presented. From a sample of 298 SySts with available optical spectra, 55% are found to emit the line. No significant preference is found among the different types. The report of the OVI{lambda}6830 Raman-scattered line in non-SySts is also discussed as well as the correlation between the Raman-scattered OVI line and X-ray emission. We conclude that the presence of the OVI Raman-scattered line still provides a strong criterion for identifying a source as a SySt.
- ID:
- ivo://CDS.VizieR/J/ApJ/740/98
- Title:
- Synchroton peak for blazars and radio galaxies
- Short Name:
- J/ApJ/740/98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We revisit the concept of a blazar sequence that relates the synchrotron peak frequency ({nu}_peak_) in blazars with synchrotron peak luminosity (L_peak_, in {nu}L_{nu}_) using a large sample of radio-loud active galactic nuclei. We present observational evidence that the blazar sequence is formed from two populations in the synchrotron {nu}_peak_-L_peak_ plane, each forming an upper edge to an envelope of progressively misaligned blazars, and connecting to an adjacent group of radio galaxies having jets viewed at much larger angles to the line of sight. When binned by jet kinetic power (L_kin_; as measured through a scaling relationship with extended radio power), we find that radio core dominance decreases with decreasing synchrotron L_peak_, revealing that sources in the envelope are generally more misaligned. We find population-based evidence of velocity gradients in jets at low kinetic powers (~10^42^-10^44.5^erg/s), corresponding to Fanaroff-Riley (FR) I radio galaxies and most BL Lac objects. These low jet power "weak-jet" sources, thought to exhibit radiatively inefficient accretion, are distinguished from the population of non-decelerating, low synchrotron-peaking (LSP) blazars and FR II radio galaxies ("strong" jets) which are thought to exhibit radiatively efficient accretion. The two-population interpretation explains the apparent contradiction of the existence of highly core-dominated, low-power blazars at both low and high synchrotron peak frequencies, and further implies that most intermediate synchrotron peak sources are not intermediate in intrinsic jet power between LSP and high synchrotron-peaking (HSP) sources, but are more misaligned versions of HSP sources with similar jet powers.
- ID:
- ivo://CDS.VizieR/J/A+A/488/867
- Title:
- Synchrotron peak frequency of 135 AGN
- Short Name:
- J/A+A/488/867
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The blazar sequence is a scenario in which the bolometric luminosity of the blazar governs the appearance of its spectral energy distribution. The most prominent result is the significant negative correlation between the synchrotron peak frequencies and the synchrotron peak luminosities of the blazar population. Observational studies of the blazar sequence have, in general, neglected the effect of Doppler boosting. We study the dependence of both the synchrotron peak frequency and luminosity with Doppler-corrected quantities. We determine the spectral energy distributions of 135 radio-bright AGN and find the best-fit parabolic function for the distribution to quantify their synchrotron emission. The corresponding measurements of synchrotron peak luminosities and frequencies are Doppler-corrected with a new set of Doppler factors calculated from variability data. The relevant correlations for the blazar sequence are determined for these intrinsic quantities.
- ID:
- ivo://CDS.VizieR/J/AJ/109/2503
- Title:
- Synthesis model in HII regions. II.
- Short Name:
- J/AJ/109/2503
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A stellar population synthesis model, suitable for comparison with Giant Extragalactic H II Regions (GEHRs), is constructed incorporating the recent developments in modeling stellar evolution by Maeder and co-workers and stellar atmospheres by Kurucz. A number of quantities suitable for comparison with broadband data of GEHRs in visible and near-infrared parts of the spectrum are synthesized in addition to the hydrogen and helium ionizing photon production rates at solar metallicities, for three scenarios of star formation - (i) instantaneous burst (IB); (ii) continuous star formation (CSF); and (iii) two bursts of star formation, with the older burst rich in red supergiants. For the IB case, evolution of color indexes shows three distinct phases - an initial steady blue phase, followed by a red bump (5-15Myr) and another steady phase with color indexes intermediate to the earlier two phases. CSF color indexes asymptotically reach peak values at ~10Myr, never reaching the reddest IB color indexes. Ionizing photon production rate falls off by an order of magnitude in 6Myr for IB, whereas it almost remains constant for the CSF model. Two-burst models with burst separations ~10Myr have properties of both IB and CSF, simultaneously producing the red IB color indexes and high ionizing photon rate, making such regions easily distinguishable using optical observations. Flat IMFs result in bluest color indexes when the massive stars are on the main sequence and reddest color indexes during the red supergiant phase of the evolving massive stars. Errors on the computed quantities due to the statistical uncertainties inherent in the process of star formation become negligible for cluster masses in excess of 10^5 M_{sun}_. Our GEHR spectra in the range 200nm to 3um are found to be in good agreement with the computations of Mas-Hesse & Kunth (1991A&AS...88..399M)
- ID:
- ivo://CDS.VizieR/J/A+AS/111/57
- Title:
- Synthetic absorption in star forming regions
- Short Name:
- J/A+AS/111/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectral evolutionary calculations have been employed in order to follow the behaviour of absorption lines in single-burst star forming regions. The model calculations are based on theoretical evolutionary tracks and model atmosphere stellar spectra at 5A resolution and they include the pre-main sequence phase. Three different metallicities have been considered; Z=0.001, 0.008 and 0.020, this range covers easily the one occupied by blue compact dwarf galaxies. This analysis focuses on the post-active burst phase and follows the evolution up to 15 million years after the episode of star formation has ceased, using an instantaneous burst of star formation. The absorption lines included are hydrogen, neutral and once ionized helium. Non-LTE absorption line profiles have been implemented to these lines, also at a 5A resolution. The equivalent widths and line profiles are studied as a function of lower and upper mass limits and slope of the mass function as well as the age. It is shown that the equivalent widths of the Balmer lines are increasing during the course of evolution, while the strength of the neutral and ionized helium lines decreases monotonically. Both the hydrogen and helium lines show high sensitivity to variations in the initial mass function (IMF). The Balmer line equivalent widths range from about 1.5 to 6.5A, depending on the IMF parameters used. As anticipated, these numbers are rather insensitive to the metallicity. Contrary to what has been claimed, the Balmer lines are prominent even if the lower mass limit is as high as 10M_{sun}_. It has been proposed that the weak hydrogen lines sometimes seen in starburst galaxies, often interpreted as evidence for a deficiency in low mass stars, could be due to the finite lifetimes of pre-main sequence stars. This analysis shows that it is very much dependent on the slope of the mass function. The equivalent width of the HeI-4471A line never exceeds 0.35A for any choice of the IMF parameters while the equivalent width of the HeII-4686A line reaches at the most 0.20A using the most top-heavy IMF. As expected, these numbers are only slightly dependent on the metallicity in the optical spectral region.
21290. Synthetic galaxy spectra
- ID:
- ivo://CDS.VizieR/J/A+A/538/A38
- Title:
- Synthetic galaxy spectra
- Short Name:
- J/A+A/538/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an optimized library of synthetic galaxy spectra that are to be used for the Gaia satellite observations of unresolved galaxies. These galaxy spectral templates are useful for the optimal performance of the unresolved galaxy classifier (UGC) software. The UGC will assign spectral classes to the observed unresolved galaxies by Gaia (classification) and estimate some of their intrinsic astrophysical parameters, which were used to create the synthetic library (parametrization). We present the new optimized synthetic library of galaxy spectra and the classification and parametrization results using the Gaia-simulated version of this library. To optimize our synthetic library, we applied the principal component analysis (PCA) method to our synthetic spectra and studied the influence of the star-formation rate parameters on the spectra, and how these agree with some typical characteristics of the galaxy spectral types. We used support vector machines (SVM) to classify and parametrize the optimal simulated spectra. The library of synthetic galaxy spectra was optimized. In this new set of synthetic spectra, overlaps in spectral energy distributions and colors are highly suppressed, while the results of UGC classification are improved.