-
S. Hubrig,
J. F. Gonzalez,
I. Ilyin,
H. Korhonen,
M. Schoeller,
I. Savanov,
R. Arlt, F. Castelli,
G. Lo Curto,
M. Briquet,
T. H. Dall
[show abstract]
[hide abstract]
ABSTRACT: The frequent presence of weak magnetic fields on the surface of spotted
late-B stars with HgMn peculiarity in binary systems has been controversial
during the two last decades.
We re-analyse available spectropolarimetric material by applying the moment
technique on spectral lines of inhomogeneously distributed elements separately.
Furthermore, we present new determinations of the mean longitudinal magnetic
field for the HgMn star HD65949 and the hotter analog of HgMn stars, the PGa
star HD19400, using FORS2 installed at the VLT. We also give new measurements
of the eclipsing system AR Aur with a primary star of HgMn peculiarity which
were obtained with the SOFIN spectropolarimeter installed at the Nordic Optical
Telescope.
We downloaded from the ESO archive the publically available HARPS spectra for
eight HgMn stars and one normal and one superficially normal B-type star
obtained in 2010. The application of the moment technique to the HARPS and
SOFIN spectra allowed us to study the presence of the longitudinal magnetic
field, the crossover effect, and quadratic magnetic fields. Results for the
HgMn star HD65949 and the PGa star HD19400 are based on a linear regression
analysis of low-resolution spectra obtained with FORS2 in spectropolarimetric
mode.
Our measurements of the magnetic field with the moment technique using
spectral lines of several elements separately reveal the presence of a weak
longitudinal magnetic field, a quadratic magnetic field, and the crossover
effect on the surface of several HgMn stars as well as normal and superficially
normal B-type stars. Furthermore, our analysis suggests the existence of
intriguing correlations between the strength of the magnetic field, abundance
anomalies, and binary properties.
08/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: The recent availability of ESO's 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.
04/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: We describe and model emission lines in the first overtone band of CO in the
magnetic Herbig Ae star HD 101412. High-resolution CRIRES spectra reveal
unusually sharp features which suggest the emission is formed in a thin disk
centered at 1 AU with a width 0.32 AU or less. A wider disk will not fit the
observations. Previous observations have reached similar conclusions, but the
crispness of the new material brings the emitting region into sharp focus.
12/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: In spite of large overabundances of Xe II observed in numerous
mercury-manganese (HgMn) stars, Xe II oscillator strengths are only available
for a very limited number of transitions. As a consequence, several
unidentified lines in the spectra of HgMn stars could be due to Xe II. In
addition, some predicted Xe II lines are redshifted by about 0.1 A from stellar
unidentified lines, raising the question about the wavelength accuracy of the
Xe II line data available in the literature. For these reasons we investigated
the Xe II lines lying in the 3900-4521 A, 4769-7542 A, and 7660-8000 A spectral
ranges of four well-studied HgMn stars. We compared the Xe II wavelengths
listed in the NIST database with the position of the lines observed in the
high-resolution UVES spectrum of the xenon-overabundant, slowly rotating HgMn
stars HR 6000, and we modified them when needed. We derived astrophysical
oscillator strengths for all the Xe II observed lines and compared them with
the literature values, when available. In this framework, we performed a
complete abundance analysis of HD 71066, while we relied on our previous works
for the other stars. We find that all the lines with wavelengths related to the
6d and 7s energy levels have a corresponding unidentified spectral line,
blueshifted by the same quantity of about 0.1 A in all the four stars, so that
we identified these lines as coming from Xe II and modified their NIST
wavelength value according to the observed stellar value. We find that the Xe
II stellar oscillator strengths may differ from one star to another from 0.0
dex to 0.3 dex. We adopted the average of the oscillator strengths derived from
the four stars as final astrophysical oscillator strength.
01/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: The spectra of B-type and early A-type stars show numerous unidentified lines in the whole optical range, especially in the 5100 - 5400 A interval. Because Fe II transitions to high energy levels should be observed in this region, we used semiempirical predicted wavelengths and gf-values of Fe II to identify unknown lines. Semiempirical line data for Fe II computed by Kurucz are used to synthesize the spectrum of the slow-rotating, Fe-overabundant CP star HR 6000. We determined a total of 109 new 4f levels for Fe II with energies ranging from 122324 cm^-1 to 128110 cm^-1. They belong to the Fe II subconfigurations 3d^6(^3P)4f (10 levels), 3d^6(^3H)4f (36 levels), 3d^6(^3F)4f (37 levels), and 3d^6(^3G)4f (26 levels). We also found 14 even levels from 4d (3 levels), 5d (7 levels), and 6d (4 levels) configurations. The new levels have allowed us to identify more than 50% of the previously unidentified lines of HR 6000 in the wavelength region 3800-8000 A. Tables listing the new energy levels are given in the paper; tables listing the spectral lines with loggf>/=-1.5 that are transitions to the 4f energy levels are given in the Online Material. These new levels produce 18000 lines throughout the spectrum from the ultraviolet to the infrared. Comment: Paper accepted by A&A for publication
06/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: We present high-resolution, high signal-to-noise UVES spectra of AO Vel, a quadruple system containing an eclipsing BpSi star. From these observations we reconstruct the spectra of the individual components and perform an abundance analysis of all four stellar members. We found that all components are chemically peculiar with different abundances patters. In particular, the two less massive stars show typical characteristics of HgMn stars. The two most massive stars in the system show variable line profiles indicating the presence of chemical spots. Given the youth of the system and the notable chemical peculiarities of their components, this system could give important insights in the origin of chemical anomalies. Comment: 8 pages, 7 figures, 1 appendix. To be published in the Monthly Notices of the Royal Astronomical Society
01/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: The analysis of the high-resolution UVES spectra of the CP stars HR 6000 and 46 Aql revealed the presence of an impressive number of unidentified lines, in particular in the 5000 - 5400 A region. Because numerous 4d-4f transitions of FeII lie in this spectral range, and because both stars are iron overabundant, we investigated whether the unidentified lines can be due to FeII. ATLAS12 model atmospheres with parameters [13450K, 4.3] and [12560K, 3.8] were computed for the individual abundances of HR 6000 and 46 Aql, respectively, in order to use the stars as spectroscopic sources to identify FeII lines and to determine FeII gf-values. After having identified several unknown lines in the stellar spectra as due to (3H)4d - (3H)4f transitions of FeII, we derived stellar log gf's for them by comparing observed and computed profiles. The energies of the upper levels were assigned on the basis of both laboratory iron spectra and predicted energy levels. We fixed 21 new levels of FeII with energies between 122910.9 cm^-1 and 123441.1 cm^-1. They allowed us to add 1700 new lines to the Fe II line list in the range 810 - 15011 A. Comment: accepted by Astronomy and Astrophysics -- The abstract is shortened here. Note: This study is the result of a collaboration with S. Johansson, who unfortunately left us before this paper started to be written
09/2009;
-
[show abstract]
[hide abstract]
ABSTRACT: Large abundance anomalies have been previously detected in Horizontal Branch B-type stars. We present the first high resolution study of isotopic anomalies and chemical abundances in six Horizontal Branch B-type stars in globular clusters NGC6397 and NGC6752 and compare them to those observed in HgMn stars. We obtained high-resolution (up to R~115000) UVES spectra of a representative sample of six B-type stars (T183, T191, T193, B652, B2151, B2206). It is the first time an abundance analysis is performed for all elements for which spectral lines were detected in UVES spectra of Horizontal Branch B-type stars. Our study of these stars revealed no signs of He isotopic anomalies which would produce a ^3He/^4He ratio different from the solar one. The isotopic anomaly of Ca is detected in all six studied stars. The chemical abundance analysis reveals an overabundance over the solar values of P, Ti, Mn, Fe, and Y and an overabundance over the cluster metallicity of Mg, Ca, and Cr. This behaviour is very similar in all six studied stars of both clusters with a few exceptions: The Na abundance is by more than 1.4dex larger than the cluster metallicity in B652, and by more than 0.8dex larger than the cluster metallicity in B2206; the Co abundance is 1.0dex over the solar abundance for T191, while Zr is overabundant over the solar abundance by 0.4dex in B2206. No lines of Hg or other heavy elements were observed in the spectra. Weak emission lines of Ti II, similar to those frequently observed in HgMn stars were discovered in one Horizontal Branch B-type star T191. Further, we detected a radial velocity change of 0.9km s^-1 from one night to the next for T183 and 0.4km s^-1 for B2151.
04/2009;
-
[show abstract]
[hide abstract]
ABSTRACT: The analysis of the high-resolution UVES spectra of the chemically peculiar stars HR6000 and 46 Aql has revealed the presence of an impressive number of unidentified lines, mostly concentrated in the regions 4404-4411 Å and 5100-5300 Å. Almost all of the unidentified lines are the same in both stars, which both have an iron abundance enhancement of the order of +0.7 dex over the solar value. The parameters adopted for HR 6000 and 46 Aql are Teff=12850 K, log g=4.1 and Teff=12750 K, log g=3.8, respectively. We show that some of the unknown lines can be identified as high-excitation (lower EP13eV) FeII and that most of them appear as unclassified lines in laboratory iron spectra.
Journal of Physics Conference Series 12/2008; 130(1):012003.
-
[show abstract]
[hide abstract]
ABSTRACT: We review the classical observational results for isotopic abundance variations for several elements in CP stars. We concentrate on the "newest" anomaly, in calcium. The cosmically very rare isotope, Ca-48 can rival and even dominate the more common, alpha nuclide, Ca-40. Relevant examples are found in the hot, non-magnetic HgMn stars, and the field horizontal-branch star, Feige 86. The calcium anomaly is also present in cool, magnetic stars, including the notorious HD 101065, Przybylski's star.
12/2007;
-
[show abstract]
[hide abstract]
ABSTRACT: We confirm that wavelengths shifts in the Ca II infrared triplet of CP stars are due to the rare, heavy isotope 48Ca. We have measurements of the previously difficult component λ8542, as well as additional measurements of all three components.
The shifts occur in a wide variety of CP stars, ranging from cool CP2 types to the hotter CP3 stars. The relative proportions
of the Ca isotopes appear to vary from terrestrial to nearly pure 48Ca.
11/2007: pages 269-270;
-
[show abstract]
[hide abstract]
ABSTRACT: UVES spectra of the very young (~10^7 years) peculiar B-type star HR 6000 were analyzed in the near-UV and visual spectral regions (3050-9460 A) with the aim to extend to other spectral ranges the study made previously in the UV using IUE spectra. Stellar parameters Teff=12850K, logg=4.10, and xi=0km/s, as determined from H_beta, H_gamma, H_delta Balmer profiles and from the Fe I, Fe II ionization equilibrium, were used to compute an individual abundances ATLAS12 model. We identified spectral peculiarities and obtained final stellar abundances by comparing observed and computed equivalent widths and line profiles. The adopted model fails to reproduce the (b-y) and c color indices. The spectral analysis has revealed: the presence of emission lines for Mn II, Cr II, and Fe II; isotopic anomalies for Hg, Ca; the presence of interstellar lines of Na I at lambda lambda 3302.3, 3302.9, 5890, 5896 A, and of K I at 7665, 7699 A; the presence of a huge quantity of unidentified lines, which we presume to be mostly due to Fe II transitions owing to the large Fe overabundance amounting to [+0.7]. The main chemical peculiarities are an extreme overabundance of Xe, followed by those of Hg, P, Y, Mn, Fe, Be, and Ti. The most underabundant element is Si, followed by C, N, Al, S, Mg, V, Sr, Co, Cl, Sc, and Ni. The silicon underabundance [-2.9] is the lowest value for Si ever observed in any HgMn star. The observed lines of He I can not be reproduced by a single value of the He abundance, but they require values ranging from [-0.8] to [-1.6]. Furthermore, when the observed and computed wings of He I lines are fitted, the observed line cores are much weaker than the computed ones. From the present analysis we infer the presence of vertical abundance stratification for He, Mn, and possibly also P. Comment: 14 pages, 8 figures, 6 tables, accepted for publication in A&A
09/2007;
-
[show abstract]
[hide abstract]
ABSTRACT: Large wavelength shifts of infrared triplet lines of Ca ii have been observed in the spectra of HgMn and magnetic Ap stars. They have been attributed to the heavy calcium isotopes, including 48Ca. One member of the triplet, λ8542, had been either unavailable, or of poor quality in earlier spectra. The present material shows conclusively that the stellar λ8542 shifts are consistent with an interpretation in terms of 48Ca. We find no relation between isotopic shifts of the Ca ii triplet lines, and those of Hg iiλ3984. There is a marginal indication that the shifts are anticorrelated with the surface field strengths of the magnetic stars. We see sparse evidence for 48Ca in other chemically peculiar stars, for example, Am stars, metal-poor stars or chemically peculiar red giants. However, the sample is still very small, and the wavelengths of all three triplet lines, including those in the Sun, show slight positive shifts with respect to terrestrial positions.Some profiles of the Ca ii infrared triplet in the magnetic stars show extensive wings beyond a well-defined core. We can obtain reasonable fits to these profiles using a stratified calcium abundance similar to that used by previous workers. There is no indication that either the stratification or the Zeeman effect significantly disturbs the measurement of isotope shifts.
Monthly Notices of the Royal Astronomical Society 05/2007; 377(4):1579 - 1587. · 4.90 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present the results of a high spectral resolution study of a few spectroscopic binaries with HgMn primary stars. We detect for the first time in the spectra of HgMn stars that for many elements the line profiles are variable over the rotation period. The strongest profile variations are found for the elements Pt, Hg, Sr, Y, Zr, Mn, Ga, He and Nd. The slight variability of He and Y is also confirmed from the study of high resolution spectra of another HgMn star, alpha And. Comment: 2 pages, 2 figures, to appear in "Precision Spectroscopy in Astrophysics"
03/2007;
-
[show abstract]
[hide abstract]
ABSTRACT: New opacity distribution functions (ODFs) for several metallicities have been computed. The main improvements upon previous ODFs computed by Kurucz (1990) are: (1) the replacement of the solar abundances from Anders & Grevesse (1989) with those from Grevesse & Sauval (1998); (2) the replacement of the TiO lines provided by Kurucz (1993) with the TiO lines from Schwenke (1998), as distributed by Kurucz (1999a); (3) the addition of the H2O lines from Partridge & Schwenke (1997) as distributed by Kurucz (1999b); (4) the addition of the HI-HI and HI-H+ quasi-molecular absorptions near 1600 A and 1400 A computed according to Allard et al. (1998). Other minor improvements are related with some changes in a few atomic and molecular data. New grids of ATLAS9 model atmospheres for Teff from 3500K to 50000K and logg from 0.0 dex to 5.0 dex have been computed for several metallicities with the new ODFs. Preliminary comparisons of the results from the old and new models have shown differences in the energy distributions of stars cooler than 4500K, in the ultraviolet energy distribution of metal-poor A-type stars, in the U-B and u-b color indices for Teff<7000K and in all the color indices for Teff<4250K.
06/2004;
-
[show abstract]
[hide abstract]
ABSTRACT: We compare the results of Balmer-line calculations using recent theory and improved computational algorithms with those from the widely-used SYNTHE and BALMER9 routines. The resulting profiles are mostly indistinguishable. Good fits to the normalized solar Balmer lines H$\alpha$ through H$\delta$ are obtained (apart from the cores) using the recent unified-broadening calculations by Barklem and his coworkers provided that some adjustment for the continuum is performed. We discuss a surprising linearity with temperature of the Balmer line profiles in dwarfs. Comment: Submitted to Astronomy and Astrophysics Better figures at http://astro.lsa.umich.edu/users/cowley
01/2002;
-
[show abstract]
[hide abstract]
ABSTRACT: New opacity distribution functions (ODF) have been computed for use with
the ATLAS9 model atmosphere code of Kurucz. One of the improvements upon
the Kurucz (\cite{kur90}) ODFs is the addition to the line blanketing of
the Lyman-alpha H-H and H-H+ quasi-molecular absorptions near
1600 Å and 1400 Å. New-ODF fluxes are expected to reproduce
the ultraviolet observations of lambda Boo stars and metal-poor A-type
stars in a more realistic way than previous computations did. In this
paper we compare low- and high-resolution IUE observations of lambda Boo
(HD 125162, HR 5351) with fluxes and synthetic spectra based on ATLAS9
models and new-ODFs, which were computed for [M/H]=-2.0 for all the
elements, except CNO. For C, N, and O, abundances log
(Nelem/Ntot) equal to -3.85, -3.99, and -3.11,
respectively, were adopted. We selected lambda Boo in order to compare
results from the new-ODFs with those from Allard et al.
(\cite{allar98a}, \cite{allar98b}), who tested their semi-classical
computations of the H-H and H-H+ quasi-molecular absorptions
on this star. The analysis of the IUE high-resolution spectrum has shown
that lines of H2 are a very important source of line opacity
for lambda Boo shortward 1600 Å. When both atomic and molecular
lines are considered, the slope of the observed energy distribution is
well reproduced in the whole region 1300-3000 Å by the new-ODF
model, but the H-H quasi-molecular absorption at 1600 Å is
computed about 10% too strong. The fit of the low-resolution IUE image
SWP17872 to a small grid of new-ODF models gives parameters
Teff= 8650 K, log g=4.0, while the fit of the high-resolution
image SWP42081, rebinned at the low resolution wavelength step size,
gives parameters Teff=8500 K, log g=4.0. These last
parameters are in close agreement with Teff=8550 K, log g=4.1
obtained by fitting the visible energy distribution. The different IUE
images are discussed.
Astronomy and Astrophysics 05/2001; 372:260-275. · 4.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Aims. The analysis of the high-resolution UVES spectra of the CP stars HR 6000 and 46 Aql has revealed the presence of an impressive number of unidentified lines, in particular in the 5000–5400 Å region. Because numerous 4d–4f transitions of FeII lie in this spectral range, and because both stars are iron overabundant, we investigate whether the unidentified lines are FeII. Methods. ATLAS12 model atmospheres with parameters $T_{\rm eff}$ = 13 450 K, $\log\,g$ = 4.3 and $T_{\rm eff}$ = 12 560 K, $\log\,g$ = 3.8 were computed for the individual abundances of the stars HR 6000 and 46 Aql, respectively, to use them as spectroscopic sources to identify FeII lines and determine FeII gf-values. After identifying several unknown lines in the stellar spectra as ($^{3}$H)4d-($^{3}$H)4f transitions of FeII, we derived astrophysical $\log\,gf$-values for them. The energies of the upper levels were assigned on the basis of both laboratory iron spectra and predicted energy levels. Results. We determined 21 new levels of FeII with energies between 122 910.9 cm$^{-1}$ and 123 441.1 cm$^{-1}$. They allowed us to add 1700 new lines to the FeII linelist in the wavelength range 810-15 011 Å. Many of these lines are sufficiently strong to contribute to the spectra of Population I late B-type stars, even when their iron abundance is subsolar. In the 5000–6000 Å region discussed in this paper, the astrophysical and computed $\log\,gf$-values show good general agreement and greatly improve the synthetic spectrum of both HR 6000 and 46 Aql. However, many features remain unidentified indicating that further work to classify FeII high energy levels has still to be done
http://dx.doi.org/10.1051/0004-6361/200912518.
-
[show abstract]
[hide abstract]
ABSTRACT: We present an empirical model-atmosphere investigation of missing Fe I opacity. Houdashelt et al. ([CITE]) estimated that if Dragon & Mutschlecner ([CITE]) Fe I cross sections used in the MARCS model atmospheres (Gustafsson et al. [CITE]) were replaced by the Bautista ([CITE]) cross sections the solar continuous flux would be reduced by 15% in the near ultraviolet. That would imply systematic errors in models for F, G, and K stars. As a consequence, since ATLAS9 (Kurucz [CITE]) uses an approximation to the same Dragon & Mutschlecner ([CITE]) opacities, there should also be similar systematic errors in ATLAS9 models that required this investigation. Bound-free Fe I cross sections computed by Bautista ([CITE]) in the framework of the IRON Project were used to generate the continuous Fe I absorption coefficient. It was incorporated in the Kurucz ([CITE]) ATLAS9 code, in place of that currently used, which is based on approximate cross sections by Kurucz. By combining Opacity Distribution Functions (ODFs) computed without the contribution of Fe I autoionization lines with the new Fe I absorption coefficient which is crowded with autoionization resonances, we obtained solar metallicity model atmospheres and energy distributions for several combinations of $T_{\rm eff}$ and $\log\,g$. The comparison of these models with the standard ATLAS9 models has shown that there are no differences in the $T$-$\tau_{\rm Ross}$ relations, while there are some changes in the energy distributions for $T_{\rm eff}$ $\le$ 7000 K, but limited to small wavelength regions around 2150 Å, where Kurucz has less opacity, and 3350 Å, where Bautista has less opacity. The differences are of the order of 25% and less than 10%, respectively. That around 2150 Å disappears for $T_{\rm eff}$ $\le$ 5500 K owing to the fall of the emergent flux at these wavelengths in cool stars. This behaviour is independent of the gravity. The explanation is that our line list actually has more autoionizing opacity than Bautista's but it is treated as bound-bound line opacity rather than as bound-free opacity.
http://dx.doi.org/10.1051/0004-6361:20040079.
-
[show abstract]
[hide abstract]
ABSTRACT: We present a high resolution spectral atlas of the HgMn star HD 175640 covering the 3040-10 000 Å region. UVES spectra observed with 90 000-110 000 resolving power and signal to noise ratio ranging from 200 to 400 are compared with a synthetic spectrum computed with the SYNTHE code (Kurucz [CITE]). The model atmosphere is an ATLAS12 model (Kurucz [CITE]) with parameters $T_{{\rm eff}}$ $=$ 12 000 K, $\log~g$ $=$ 3.95, $\xi$ = 0 km s$^{-1}$. The stellar individual abundances in ATLAS12 were derived from an iterative procedure. The starting atomic line lists downloaded from the Kurucz website have been improved and extended by examining different sources in the literature and by comparing the computed profiles with the observed spectrum. The high quality of the data allowed us to study the isotopic and hyperfine structure for several lines of $\ion{Mn}{ii}$, $\ion{Ga}{ii}$, $\ion{Ba}{ii}$, $\ion{Pt}{ii}$, $\ion{Hg}{i}$, and $\ion{Hg}{ii}$. Numerous weak emission lines from $\ion{Cr}{ii}$ and $\ion{Ti}{ii}$ have been identified in the red part of the spectrum, starting at $\approx$$\lambda$ 5847 Å. Two emission lines of $\ion{C}{i}$ (mult. 10, mult. 9) have been observed for the first time. All $\ion{Cr}{ii}$ and $\ion{Ti}{ii}$ emission lines originate from the high excitation states ($\chi_{{\rm low}}$ $\ga$ 89 000 cm$^{-1}$ for $\ion{Cr}{ii}$ and $\chi_{{\rm low}}$ $\ga$ 62 000 cm$^{-1}$ for $\ion{Ti}{ii}$) with large transition probabilities ($\log~gf >-$1.00). The synthetic spectrum superimposed on the observed spectrum as well as the adopted improved atomic line lists are available at the CDS and http://wwwuser.oat.ts.astro.it/castelli/stars.html. An extended discussion on each identified ion and related atomic data is available both on the quoted website and in an electronic Appendix to the paper.
http://dx.doi.org/10.1051/0004-6361:20041011.
