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Register a new userLine identification in high-resolution, near-infrared CRIRES spectra of chemically peculiar and Herbig Ae stars
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Added by
Markus Sch\\\"oller
Publication date
2012
fields
Physics
and research's language is
English
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The recent availability of ESOs high-resolution spectrograph CRIRES offers now the opportunity to study numerous spectral features in the near-IR in intermediate-mass main-sequence and pre-main-sequence stars. High-resolution CRIRES spectra were obtained in three spectral regions, two regions around 1mu and one region around 1.57mu containing magnetically sensitive Fe I lines. The largest number of near-IR spectral features was detected and identified in the well-studied magnetic Ap star gamma Equ. Nearly 30% of the spectral lines in the Ap star HD154708, with one of the strongest magnetic fields known among the Ap stars of the order of 25kG, remain unidentified due to a lack of atomic data. Only very few lines belonging to the rare earth element group have been identified in both Ap stars. A number of spectral lines including the Ce III and Dy II lines appear magnetically split due to the presence of a strong magnetic field in their atmospheres. Variable behaviour of lines of the elements He, N, Mg, Si, and Fe over the rotation period in the spectra of HD101412 confirm our previous finding of variability in the optical region. Due to the very fast rotation of 51Oph, only a few spectral lines have been identified with certainty.
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New instrumental capabilities and the wealth of astrophysical information extractable from the near-infrared wavelength region have led to a growing interest in the field of high resolution spectroscopy at 1-5 mu. We aim to provide a library of observed high-resolution and high signal-to-noise-ratio near-infrared spectra of stars of various types throughout the Hertzsprung-Russell diagram. This is needed for the exploration of spectral features in this wavelength range and for comparison of reference targets with observations and models. High quality spectra were obtained using the CRIRES near-infrared spectrograph at ESOs VLT covering the range from 0.97 to 5.3 mu at high spectral resolution. Accurate wavelength calibration and correction for of telluric lines were performed by fitting synthetic transmission spectra for the Earths atmosphere to each spectrum individually. We describe the observational strategy and the current status and content of the library which includes 13 objects. The first examples of finally reduced spectra are presented. This publication will serve as a reference paper to introduce the library to the community and explore the extensive amount of material.
Accretion is the prime mode of star formation, but the exact mode has not yet been identified in the Herbig Ae/Be mass range. We provide evidence that the the maximum variation in mass-accretion rate is reached on a rotational timescale, which suggests that rotational modulation is the key to understanding mass accretion. We show how spectropolarimetry is uniquely capable of resolving the innermost (within 0.1 AU) regions between the star and the disk, allowing us to map the 3D geometry of the accreting gas, and test theories of angular momentum evolution. We present Monte Carlo line-emission simulations showing how one would observe changes in the polarisation properties on rotational timescales, as accretion columns come and go into our line of sight.
We present FEROS high-resolution (R~45000) optical spectroscopy of 34 Herbig Ae/Be star candidates with previously unknown or poorly constrained spectral types. Within the sample, 16 sources are positionally coincident with nearby (d<250 pc) star-forming regions (SFRs). All the candidates have IR excess. We determine the spectral type and luminosity class of the sources, derive their radial and rotational velocities, and constrain their distances employing spectroscopic parallaxes. We confirm 13 sources as Herbig Ae/Be stars and find one classical T Tauri star. Three sources are emission line early-type giants and may be Herbig Ae/Be stars. One source is a main-sequence A-type star. Fourteen sources are post-main-sequence giant and supergiant stars. Two sources are extreme emission-line stars. Most of the sources appear to be background stars at distances over 700 pc. We show that high-resolution optical spectroscopy is a crucial tool for distinguishing young stars from post-main sequence stars in samples taken from emission-line star catalogs based on low-resolution spectroscopy. Within the sample, 3 young stars (CD-38 4380, Hen 3-1145, and HD 145718) and one early-type luminosity class III giant with emission lines (Hen 3-416) are at distances closer than 300 pc and are positionally coincident with a nearby SFR. These 4 sources are likely to be nearby young stars and are interesting for follow-up observations at high-angular resolution. Furthermore, seven confirmed Herbig Ae/Be stars at d>700 pc (Hen 2-80, Hen 3-1121 N&S, HD 313571, MWC 953, WRAY 15-1435, and Th 17-35) are inside or close (<5) to regions with extended 8 micron continuum emission and in their 20 vicinity have astronomical sources characteristic of SFRs. These 7 sources are likely to be members of SFRs. These regions are attractive for future studies of their stellar content.
We report near-infrared photometric measurements of 35 Herbig Ae/Be candidate stars obtained with direct imaging and aperture photometry. Observations were made through the broadband J, H, and K filters, with each source imaged in at least one of the wavebands. We achieved subarcsecond angular resolution for all observations, providing us with the opportunity to search for close binary candidates and extended structure. The imaging revealed five newly identified binary candidates and one previously resolved T Tauri binary among the target sources with separations of <~2.5. Separate photometry is provided for each of the binary candidate stars. We detect one extended source that has been identified as a protoplanetary nebula. Comparing our magnitudes to past measurements yields significant differences for some sources, possibly indicating photometric variability. H-band finding charts for all of our sources are provided to aid follow-up high-resolution imaging.
We present near-IR (J,H,Ks) photometry for 27 of the 28 candidate Herbig Ae/Be stars in the Small and Large Magellanic Clouds identified via the EROS1 and EROS2 surveys as well as near-contemporaneous optical (H-alpha) spectroscopy for 21 of these 28 candidates. Our observations extend previous efforts to determine the evolutionary status of these objects. We compare the IR brightness and colors of a subset of our sample with archival ground-based IR data and find evidence of statistically significant photometric differences for ELHC 5, 7, 12, 18, and 21 in one or more filter. In all cases, these near-IR photometric variations exhibit a grey color as compared to earlier epoch data. The ~1 magnitude IR brightening and minimal change in the H-alpha emission strength we observe in ELHC 7 is consistent with previous claims that it is a UX Ori type HAe/Be star, which is occasionally obscurred by dust clouds. We also detect a ~1 magnitude IR brightening of ELHC 12, but find little evidence of a similar large-scale change in its H-alpha line strength, suggesting that its behavior could also be caused by a UX Ori-like event. The ~0.5 magnitude IR variability we observe for ELHC 21, which also exhibited little evidence of a change in its H-alpha emission strength, could conceivably be caused by a major recent enhancement in the density of the inner disk region of a classical Be star. We also report the first near-IR photometry for two ESHC stars and the first H-alpha spectroscopy for one ELHC and five ESHC stars. Although H-alpha emission is detected in all of these new observations, they do not exhibit a strong near-IR excess. It is therefore possible that many of these objects may be classical Be stars rather than Herbig Ae/Be stars.
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