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Register a new userAlgorithm for removing secondary lines blended with Balmer lines in synthetic spectra of massive stars
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Added by
Celia Rosa Fierro-Santill\\'an
Publication date
2021
fields
Physics
and research's language is
English
Authors
Celia Rosa Fierro-Santillan
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No Arabic abstract
In order to measure automatically the equivalent width of the Balmer lines in a database of 40,000 atmosphere models, we have developed a program that mimics the work of an astronomer in terms of identifying and eliminating secondary spectral lines mixed with the Balmer lines. The equivalent widths measured have average errors of 5 percent, which makes them very reliable. As part of the FITspec code, this program improves the automatic adjustment of an atmosphere model to the observed spectrum of a massive star.
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An analysis of H alpha and H beta spectra in a sample of 30 cool dwarf and subgiant stars is presented using MARCS model atmospheres based on the most recent calculations of the line opacities. A detailed quantitative comparison of the solar flux spectra with model spectra shows that Balmer line profile shapes, and therefore the temperature structure in the line formation region, are best represented under the mixing length theory by any combination of a low mixing-length parameter alpha and a low convective structure parameter y. A slightly lower effective temperature is obtained for the sun than the accepted value, which we attribute to errors in models and line opacities. The programme stars span temperatures from 4800 to 7100 K and include a small number of population II stars. Effective temperatures have been derived using a quantitative fitting method with a detailed error analysis. Our temperatures find good agreement with those from the Infrared Flux Method (IRFM) near solar metallicity but show differences at low metallicity where the two available IRFM determinations themselves are in disagreement. Comparison with recent temperature determinations using Balmer lines by Fuhrmann (1998, 2000), who employed a different description of the wing absorption due to self-broadening, does not show the large differences predicted by Barklem et al. (2000). In fact, perhaps fortuitously, reasonable agreement is found near solar metallicity, while we find significantly cooler temperatures for low metallicity stars of around solar temperature.
We discovered non-stellar Balmer absorption lines in two many-narrow-trough FeLoBALs (mntBALs) by the near-infrared spectroscopy with Subaru/CISCO. Presence of the non-stellar Balmer absorption lines is known to date only in the Seyfert galaxy NGC 4151, thus our discovery is the first cases for quasars. Since all known active galactic nuclei with Balmer absorption lines share characteristics, it is suggested that there is a population of BAL quasars which have unique structures at their nuclei or unique evolutionary phase.
Our knowledge of circumstellar disks has traditionally been based on studies of dust. However, gas dominates the disk mass and its study is key to understand the star and planet formation process. Spitzer can access gas emission lines in the mid-infrared, providing new diagnostics of the physical conditions in accretion disks and outflows. We have studied the spectra of 64 pre-main-sequence stars in Taurus using Spitzer/IRS observations. We have detected H2 (17.03, 28.22 $mu$m) emission in 6 objects, [Ne II] (12.81 $mu$m) in 18 objects, and [Fe II] (17.93, 25.99 $mu$m) in 7 objects. [Ne II] detections are found primarily in Class II objects. The luminosity of the [Ne II] line, is in general higher for objects known to drive jets than for those without known jets, but the two groups are not statistically distinguishable. We have searched for correlations between the line luminosities and different parameters related to the star-disk system. The [Ne II] luminosity is correlated with X-ray luminosity for Class II objects. The [NeII] luminosity is correlated with disk mass and accretion rate when the sample is divided into high and low accretors. We also find correlations between [NeII] luminosity and mid-IR continuum luminosity and with luminosity of the [O I] (6300 AA) line, the latter being an outflow tracer. [Fe II] luminosity correlates with mass accretion rate. No correlations were found between H2 luminosity and several tested parameters. Our study reveals a general trend toward accretion-related phenomena as the origin of the gas emission lines. Shocks in jets and outflowing material are more likely to play a significant role than shocks in infalling material. The role of X-ray irradiation is less prominent but still present for [Ne II], in particular for Class II sources, the lack of correlation between [Fe II] and [Ne II] points toward different emitting mechanisms.
The Stark-induced shift and asymmetry, the so-called pressure shift (PS) of $H_alpha$ and $H_beta$ Balmer lines in spectra of DA white dwarfs (WDs), as masking effects in measurements of the gravitational red shift in WDs, have been examined in detail. The results are compared with our earlier ones from before a quarter of a century (Grabowski et al. 1987, hereafter ApJ87; Madej and Grabowski 1990). In these earlier papers, as a dominant constituent of the Balmer-line-profiles, the standard, symmetrical Stark line profiles, shifted as the whole by PS-effect, were applied to all spectrally active layers of the WD atmosphere. At present, in each of the WD layers, the Stark-line-profiles (especially of $H_beta$) are immanently asymmetrical and shifted due to the effects of strong inhomogeneity of the perturbing fields in plasma. To calculate the Stark line-profiles in successive layers of the WD atmosphere we used the modified Full Computer Simulation Method (mFCSM), able to take adequately into account the complexity of local elementary quantum processes in plasma. In the case of the $H_alpha$ line, the present value of Stark-induced shift of the synthetic $H_alpha$ line-profile is about twice smaller than the previous one (ApJ87) and it is negligible in comparison with the gravitational red shift. In the case of the $H_beta$ line, the present value of Stark-induced shift of the synthetic $H_beta$ line-profile is about twice larger than the previous one. The source of this extra shift is the asymmetry of $H_beta$ peaks.
Our preliminary results from laboratory experiments studying white dwarf (WD) photospheres show a systematic difference between experimental plasma conditions inferred from measured H$beta$ absorption line profiles versus those from H$gamma$. One hypothesis for this discrepancy is an inaccuracy in the relative theoretical line profiles of these two transitions. This is intriguing because atmospheric parameters inferred from H Balmer lines in observed WD spectra show systematic trends such that inferred surface gravities decrease with increasing principal quantum number, $n$. If conditions inferred from lower-$n$ Balmer lines are indeed more accurate, this suggests that spectroscopically determined DA WD masses may be greater than previously thought and in better agreement with the mean mass determined from gravitational redshifts.
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