Chemical Peculiarities Research Articles

Chemical peculiarities of the Silurian–Ordovician and Cambrian–Vendian aquifer systems in Estonia: an overview of hydrochemical studies

The chemical composition of groundwater was studied and plausible reasons for its peculiarities were evaluated on the basis of long-term groundwater monitoring data. Fluoride and boron anomaly was distinguished in the Silurian-Ordovician aquifer system in western Estonia. The chemical type of groundwater controls the dissolution of fluorides and boron in water. Their concentrations are highest in deep groundwater having long residence time in the host rocks. The dissolution of carbonate rocks and clayey K-bentonite beds are the sources of F in groundwater. Barium anomaly in the Cambrian-Vendian aquifer system occurs in northeastern Estonia, where the intrusion of saline groundwater from the weathered crystalline basement contributes to the formation of Ba-rich groundwater. The overexploitation of fresh groundwater has resulted in the increase in groundwater salinity, however, detectable intrusion of seawater into the Cambrian-Vendian aquifer system is ruled out by the stable isotope signature.

Magnetic fields and chemical peculiarities of the very young intermediate-mass binary system HD 72106

The recently discovered magnetic Herbig Ae and Be stars may provide qualitatively new information about the formation and evolution of magnetic Ap and Bp stars. We have performed a detailed investigation of one particularly interesting binary system with a Herbig Ae secondary and a late B-type primary possessing a strong, globally ordered magnetic field. 20 high-resolution Stokes V spectra of the system were obtained with the ESPaDOnS instrument mounted on the Canada-France-Hawaii Telescope. In these observations we see clear evidence for a magnetic field in the primary, but no evidence for a magnetic field in the secondary. A detailed abundance analysis was performed for both stars, revealing strong chemical peculiarities in the primary and normal chemical abundances in the secondary. The primary is strongly overabundant in Si, Cr and other iron-peak elements, as well as Nd, and underabundant in He. The primary therefore appears to be a very young Bp star. In this context, line profile variations of the primary suggest non-uniform lateral distributions of surface abundances. Interpreting the 0.639 95 +/- 0.000 09 d variation period of the Stokes I and V profiles as the rotational period of the star, we have modelled the magnetic field geometry and the surface abundance distributions of Si, Ti, Cr and Fe using magnetic Doppler imaging. We derive a dipolar geometry of the surface magnetic field, with a polar strength B-d = 1230 G and an obliquity beta = 57 degrees. The distributions Ti, Cr and Fe are all qualitatively similar, with an elongated patch of enhanced abundance situated near the positive magnetic pole. The Si distribution is somewhat different, and its relationship to the magnetic field geometry less clear.

Magnetic fields in O-type stars measured with FORS 1 at the VLT

AbstractThe presence of magnetic fields in O-type stars has been suspected for a long time. The discovery of such fields would explain a wide range of well documented enigmatic phenomena in massive stars, in particular cyclical wind variability, Hα emission variations, chemical peculiarity, narrow X-ray emission lines and non-thermal radio/X-ray emission. Here we present the results of our studies of magnetic fields in O-type stars, carried out over the last years.

Magnetic field measurements of O stars with FORS 1 at the VLT

Context. The presence of magnetic fields in O-type stars has been suspected for a long time. The discovery of these fields would explain a wide range of well documented enigmatic phenomena in massive stars, in particular cyclical wind variability, Ha emission variations, chemical peculiarity, narrow X-ray emission lines, and non-thermal radio/X-ray emission. Aims. To investigate the incidence of magnetic fields in O stars, we acquired 38 new spectropolarimetric observations with FORS 1 (FOcal Reducer low dispersion Spectrograph) mounted on the 8-m Kueyen telescope of the VLT. Methods. Spectropolarimetric observations were obtained at different phases for a sample of 13 O stars. Ten stars were observed in the spectral range 348-589 nm, HD36879 and HD148937 were observed in the spectral region 325-621 nm, and HD155806 was observed in both settings. To prove the feasibility of the FORS1 spectropolarimetric mode for the measurements of magnetic fields in hot stars, we present in addition 12 FORS 1 observations of the mean longitudinal magnetic field in theta(1) OriC and compare them with measurements obtained with the MuSiCoS, ESPaDOnS, and Narval spectropolarimeters. Results. Most stars in our sample, which were observed on different nights, show a change of the magnetic field polarity, but a field at a significance level of 3 sigma was detected in only four stars, HD36879, HD148937, HD152408, and HD164794. The largest longitudinal magnetic field, = -276 +/- 88 G, was detected in the Of?p star HD148937. We conclude that large-scale organized magnetic fields with polar field strengths larger than 1 kG are not widespread among O-type stars.

HVS 7: a chemically peculiar hyper-velocity star

Context. Hyper-velocity stars are suggested to originate from the dynamical interaction of binary stars with the supermassive black hole in the Galactic centre (GC), which accelerates one component of the binary to beyond the Galactic escape velocity. Aims. The evolutionary status and GC origin of the hyper-velocity star SDSS J113312.12+010824.9 (aka HVS 7) is constrained from a detailed study of its stellar parameters and chemical composition. Methods. High-resolution spectra of HVS 7 obtained with UVES on the ESO VLT were analysed using state-of-the-art NLTE/LTE modelling techniques that can account for a chemically-peculiar composition via opacity sampling. Results. Instead of the expected slight enrichments ofα-elements and near-solar iron, huge chemical peculiarities of all elements are apparent. The helium abundance is very low (<1/100 solar), C, N and O are below the detection limit, i.e they are underabundant (<1/100,.1/3 and<1/10 solar). Heavier elements, however, are overabundant: the iron group by a factor of∼10, P, Co and Cl by factors∼40, 80 and 440 and rare-earth elements and mercury even by∼10 000. An additional finding, relevant also for other chemic ally peculiar stars are the large NLTE effects on abundances of Tiii and Feii (∼0.6‐0.7 dex). The derived abundance pattern of HVS 7 is characteristic for the class of chemical peculiar magnetic B stars on the main sequence. The chemical composition and high projected rotation velocity v sin i= 55±2 km s −1 render a low mass nature of HVS 7 as a blue horizontal branch star unlikely. Conclusions. Such a surface abundance pattern is caused by atomic diffusion in a possibly magnetically stabilised, non-convective atmosphere. Hence all chemical information on the star’s plac e of birth and its evolution has been washed out. High precision astrometry is the only means to validate a GC origin for HVS 7.

New insights into the nature of the peculiar star θ Carinae

Context. θ Carinae belongs to a group of peculiar early-type stars (OBN) with enhanced nitrogen and carbon deficiency. It is also known as a binary system, but it is not clear yet whether the chemical anomalies can be explained by mass transfer between the two components. On the basis of the previously reported spectral variability of a few metal lines it may be expected that θ Car possesses a weak magnetic field. Aims. A study of the physical nature of this hot massive binary which is furthermore a well-known blue straggler lying ∼2 mag above the turnoff of the young open cluster IC 2602 is important to understand the origin of its strong chemical anomalies. Methods. We acquired high resolution spectroscopic and low resolution spectropolarimetric observations to achieve the following goals: a) to improve the orbital parameters to allow a more in-depth discussion on the possibility of mass transfer in the binary system; b) to carry out a non-local thermodynamic equilibrium (NLTE) abundance analysis; and c) to search for the presence of a magnetic field. Results. The study of the radial velocities using CORALIE spectra allowed us to significantly improve the orbital parameters. A comparative NLTE abundance analysis was undertaken for θ Car and two other early B-type stars with recently detected magnetic fields, τ Sco and ξ 1 CMa. The analysis revealed significantly different abundance patterns: a one-order-of-magnitude nitrogen overabundance and carbon depletion was found in θ Car, while the oxygen abundance is roughly solar. For the stars ξ 1 CMa and τ Sco the carbon abundance is solar and, while an N excess is also detected, it is of much smaller amplitude (0.4−0.6 dex). Such an N overabundance is typical of the values already found for other slowly-rotating (magnetic) B-type dwarfs. For θ Car, we attribute instead the chemical peculiarities to a past episode of mass transfer between the two binary components. The results of the search for a magnetic field using FORS 1 at the VLT consisting of 26 measurements over a time span of ∼1.2 h are rather inconclusive: only few measurements have a significance level of 3σ. Although we detect a periodicity of the order of ∼8.8 min in the dataset involving the measurements on all hydrogen Balmer lines with the exception of the Hα and Hβ lines, these results have to be confirmed by additional time-resolved magnetic field observations.

Bridgman Crystal Growth and Structure Refinement of YbPdGe and YbPtGe – Two Different Superstructures of the KHg2 Type

AbstractWell shaped single crystals of the equiatomic germanides YbPdGe and YbPtGe were synthesized from the elements using the Bridgman technique. The samples were investigated by X‐ray powder and single crystal diffraction: YbAuSn type, Imm2, a = 433.4(2), b = 2050.6(6), c = 752.6(2) pm, wR2 = 0.0723, 1551 F2 values, 58 variables for YbPdGe and TiNiSi type, Pnma, a = 686.32(9), b = 430.47(9), c = 751.02(8) pm, wR2 = 0.0543, 379 F2 values, 20 variables for YbPtGe. Both germanides crystallize with different superstructure variants of the KHg2 type, resulting from different stacking of the puckered Pd3Ge3 and Pt3Ge3 hexagons. While only Pt–Ge interactions occur in the [PtGe] polyanionic network of YbPtGe, weak interlayer Pd–Pd (297 pm) and Ge–Ge (275 pm) interactions occur in YbPdGe. The crystal chemical peculiarities are discussed in the light of the different superstructure formed.

Intercalation Induced Electret Effect in GaSe and InSe Crystals: Experiment and Theory

Intercalation of gallium and indium selenide crystals by nickel initiates their electret polarization. The effect manifests itself at small concentrations of the intercalant. Temperature dependences of dielectric permittivity for both crystals demonstrate peaks in the same region of concentration. The effect is presumably connected with the ordering of local quasi-dipoles caused by the redistribution of intercalant atoms between octahedral and two tetrahedral positions. It is shown that a microscopic four-state model is able to reproduce a peak-like behaviour of the polarization at change of the intercalant chemical potential (concentration) and peculiarities of temperature dependences of the transverse dielectric susceptibility.

Rare earth-rich cadmium compounds RE 4 TCd (T = Co, Ru, and Rh) with Gd4RhIn type structure

The rare earth-rich cadmium compounds RE4TCd (RE = Y, La–Nd, Sm, and Gd–Tm, Lu; T = Co, Ru, and Rh) were prepared from the elements in sealed tantalum ampoules in an induction furnace. All samples were characterized by X-ray powder diffraction. The structures of Y4RuCd (a = 1362.5(1) pm), La4RuCd (a = 1415.9(1) pm), Gd4RuCd (a = 1368.8(2) pm), La4CoCd (a = 1417.9(4) pm), Gd4CoCd (a = 1356.1(1) pm), and Gd4RhCd (a = 1368.7(1) pm) were refined from single crystal X-ray diffractometer data. The RE4TCd compounds crystallize with the cubic Gd4RhIn type structure, space group F\({\bar 4}\)3m. The transition metal atoms have tricapped trigonal prismatic rare earth coordination. The trigonal prisms are condensed via common edges, forming a rigid three-dimensional network with adamantane symmetry. Voids in these networks are filled by Cd4 tetrahedra (304 pm Cd–Cd in Gd4CoCd) and polyhedra of the RE1 atoms. The crystal chemical peculiarities are briefly discussed.

Rare earth metal-rich indides RE 4IrIn (RE = Gd–Er), RE 4IrInO0.25 (RE = Gd, Er), and RE 4 TIn1–x Mg x (RE = Y, Gd; T = Rh, Ir)

The rare earth-transition metal-indides RE4IrIn (RE = Gd–Er) and the solid solutions RE4TIn1–xMgx (RE = Y, Gd; T = Rh, Ir) were prepared by arc-melting of the elements and subsequent annealing. The rare earth sesquioxides were used as oxygen source for the suboxides RE4IrInO0.25 (RE = Gd, Er). Single crystals of the indides were grown via slowly cooling of the samples and they were investigated via X-ray powder diffraction and single crystal diffractometer data: Gd4RhIn type, F\(\bar 4\)3m, a = 1372.3(6) pm for Gd4IrIn, a = 1365.3(6) pm for Tb4IrIn, a = 1356.7(4) pm for Dy4IrIn, a = 1353.9(4) pm for Ho4IrIn, a = 1344.1(4) pm for Er4IrIn, a = 1370.3(5) pm for Y4RhIn0.54Mg0.46, a = 1375.6(5) pm for Gd4IrIn0.55Mg0.45, a = 1373.0(3) pm for Gd4IrInO0.25, and a = 1345.1(4) pm for Er4IrInO0.25. The rhodium and iridium atoms have a trigonal prismatic rare earth coordination. Condensation of the RhRE6 and IrRE6 prisms leads to three-dimensional networks which leave voids that are filled by regular In4 or mixed In4–xMgx tetrahedra. The indium (magnesium) atoms have twelve nearest neighbors (3In(Mg) + 9RE) in icosahedral coordination. The rare earth atoms build up a three-dimensional, adamantane-like network of condensed, edge and face-sharing octahedra. For Gd4IrInO0.25 and Er4IrInO0.25 the RE16 octahedra are filled with oxygen. The crystal chemical peculiarities of these rare earth rich compounds are discussed.

Possible signature of hypernova nucleosynthesis in a beryllium-rich halo dwarf

Abstract As part of a large survey of halo and thick disc stars, we found one halo star, HD 106038, exceptionally overabundant in beryllium. In spite of its low metallicity, [Fe/H]=−1.26, the star has log(Be/H) =−10.60, which is similar to the solar meteoritic abundance, log(Be/H) =−10.58. This abundance is more than 10 times higher the abundance of stars with similar metallicity and cannot be explained by models of chemical evolution of the Galaxy that include the standard theory of cosmic ray spallation. No other halo star exhibiting such a beryllium overabundance is known. In addition, overabundances of Li, Si, Ni, Y and Ba are also observed. We suggest that all these chemical peculiarities, excepting the Ba abundance, can be simultaneously explained if the star was formed in the vicinity of a hypernova.

Nitrogen enrichment, boron depletion and magnetic fields in slowly-rotating B-type dwarfs

Evolutionary models for massive stars, accounting for rotational mixing effects, do not predict any core-processed material at the surface of B dwarfs with low rotational velocities. Contrary to theoretical expectations, we present a detailed and fully-homogeneous, NLTE abundance analysis of 20 early B-type dwarfs and (sub)giants that reveals the existence of a population of nitrogen-rich and boron-depleted, yet intrinsically slowly-rotating objects. The low-rotation rate of several of these stars is firmly established, either from the occurrence of phase-locked UV wind line-profile variations, which can be ascribed to rotational modulation, or from theoretical modelling in the pulsating variables. The observational data presently available suggest a higher incidence of chemical peculiarities in stars with a (weak) detected magnetic field. This opens the possibility that magnetic phenomena are important in altering the photospheric abundances of early B dwarfs, even for surface field strengths at the one hundred Gauss level. However, further spectropolarimetric observations are needed to assess the validity of this hypothesis.

Could the Ultra–Metal‐Poor Stars be Chemically Peculiar and Not Related to the First Stars?

Chemically peculiar stars define a class of stars that show unusual elemental abundances due to stellar photospheric effects and not due to natal variations. In this paper, we compare the elemental abundance patterns of the ultra-metal-poor stars with metallicities -->[ Fe/H ] ~ ? 5 to those of a subclass of chemically peculiar stars. These include post-AGB stars, RV Tauri variable stars, and the Lambda Bootis stars, which range in mass, age, binarity, and evolutionary status, yet can have iron abundance determinations as low as -->[ Fe/H ] ~ ? 5. These chemical peculiarities are interpreted as due to the separation of gas and dust beyond the stellar surface, followed by the accretion of dust-depleted gas. Contrary to this, the elemental abundances in the ultra-metal-poor stars are thought to represent yields of the most metal-poor supernovae and, therefore, observationally constrain the earliest stages of chemical evolution in the universe. Detailed chemical abundances are now available for HE 1327?2326 and HE 0107?5240, the two extreme ultra-metal-poor stars in our Galaxy, and for HE 0557?4840, another ultra-metal-poor star found by the Hamburg/ESO survey. There are interesting similarities in their abundance ratios to those of the chemically peculiar stars; e.g., the abundances of the elements in their photospheres are related to the condensation temperature of that element. If these three stars are chemically peculiar, then their CNO abundances suggest true metallicities of -->[ X/H ] ~ ? 2 to ?4. It is important to establish the nature of these stars, since they are used as tests of the early chemical evolution of the Galaxy.

Transition Metal-centered Trigonal Prisms as BuildingUnits in RE14T3In3 (RE = Y, Ho, Er, Tm, Lu; T = Pd, Ir, Pt) and Y4IrIn

The indides RE14T3In3 (RE = Y, Ho, Er, Tm, Lu; T = Pd, Ir, Pt) and Y4IrIn were synthesized from the elements by arc-melting and subsequent annealing for crystal growth. Their structures were characterized on the basis of X-ray powder and single crystal data: Lu14Co3In3-type, space group P42/nmc, a = 970.2(1), c = 2340.7(5) pm for Y13.95Pd3In3.05, a = 959.7(1), c = 2309.0(5) pm for Ho14Pd2.95In3, a = 955.5(1), c = 2305.1(5) pm for Er14Pd3In3, a = 950.9(1), c = 2291.6(5) pm for Tm13.90Pd3In3.10, a = 944.4(1), c = 2275.5(5) pm for Lu13.93Pd3In3.07, a = 962.9(1), c = 2343.0(5) pm for Y13.86Ir2.97In3.02, a = 967.6(1), c = 2347.8(5) pm for Y13.92Pt3.05In2.91, and Gd4RhIn-type, space group F 4̅3m, a = 1368.6(2) pm for Y4IrIn. The main structural motifs are transition metal-centered trigonal prisms of the rare earth elements which are condensed to twodimensional networks in the RE14T3In3 indides and to a three-dimensional one in Y4IrIn. The indium atoms in both structure types show segregation in the metal-rich matrix, i. e. In2 dumbbells in the RE14T3In3 indides (309 pm In2-In2 in Y13.86Ir2.97In3.02) and In4 tetrahedra (322 pm In-In) in Y4IrIn. The crystal chemical peculiarities of both structure types are discussed.

Late stages of the evolution of A-type stars on the main sequence: comparison between observed chemical abundances and diffusion models for 8 Am stars of the Praesepe cluster

Aims. We aim to provide observational constraints on diffusion models that predict peculiar chemical abundances in the atmospheres of Am stars. We also intend to check if chemical peculiarities and slow rotation can be explained by the presence of a weak magnetic field. Methods. We have obtained high resolution, high signal-to-noise ratio spectra of eight previously-classified Am stars, two normal A-type stars and one Blue Straggler, considered to be members of the Praesepe cluster. For all of these stars we have determined fundamental parameters and photospheric abundances for a large number of chemical elements, with a higher precision than was ever obtained before for this cluster. For seven of these stars we also obtained spectra in circular polarization and applied the LSD technique to constrain the longitudinal magnetic field. Results. No magnetic field was detected in any of the analysed stars. HD 73666, a Blue Straggler previously considered as an Ap (Si) star, turns out to have the abundances of a normal A-type star. Am classification is not confirmed for HD 72942. For HD 73709 we have also calculated synthetic Aa photometry that is in good agreement with the observations. There is a generally good agreement between abundance predictions of diffusion models and values that we have obtained for the remaining Am stars. However, the observed Na and S abundances deviate from the predictions by 0.6 dex and ≥0.25 dex respectively. Li appears to be overabundant in three stars of our sample.

A refined analysis of the remarkable Bp star HR 6000

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.

The Disk and Environment of a Young Vega Analog: HD 169142

Wetracethediskof HD169142(A8Ve)from0.57 00 to1.4 00 (� 80Y200AUprojecteddistance)in1.1 � mscattered light with HST NICMOS coronagraphy. The azimuthally symmetric disk has a peak azimuthally medianed surface brightness (SB) of � 5 mJy arcsec � 2 at 0.57 00 from the star, and drops /r � 3 . This radial SB profile is consistent with the presence of spatially resolved PAH emission and a Meeus group I IR SED only if the inner disk is either substantially flatter than the outer disk or partially devoid of material. Analysis of new HSTACS FUVimagery in tandemwitharchivalIUEdataindicates ˙ Macc � 10 � 9 Myr � 1 .Weestimatetheageof HD169142tobe6 þ6 � 3 Myrby identifying 2MASS 18242929� 2946559, located 9.3 00 to the southwest, as a 130 mas separation weak-line T Tauri binary that is comoving with HD 169142 at the 4 � confidence level. We find no evidence for any additional stellar companion in either the ACS or Chandra ACIS-S data at r � 1 00 . HD 169142 has previously been interpreted as a slowly rotating, chemically peculiar star. However, by combining the disk inclination andv sini from the literature, we find that the star hasvequatorial � 240 km s � 1 , making it a rapid rotator, similar to Altair or Vega. The UV data for HD 169142 are consistent with gravity darkening, while the X-ray luminosity and spectrum resembles early F stars at the age of thePictoris moving group, rather than mid-A stars. In this context, spectral features previously interpreted as evidence for chemical peculiarity are more likely to reflect the presence of a strong photospheric latitudinal temperature gradient. With such a gradient, HD 169142 should closely resemble Vega at the epoch of central disk clearing. Subject headings: binaries: visual — planetary systems: protoplanetary disks — stars: individual (2MASS 18242929� 2946559, HD 22128, HD 36112, HD 142666, HD 169142, HD 220750) — stars: low-mass, brown dwarfs — stars: preYmain-sequence

Soil microbial activity and free-living nematode community in the upper soil layer of the anticline erosional cirque, Makhtesh Ramon, Israel

The physical–chemical peculiarity of soil rock formations is one of the leading factors determining diversity and abundance of soil biota. The main aim of the present research was to study soil microbial and free-living nematode abundance and diversity on different soil rock formations (basalt, sandstone, limestone, granite and gypsum) of the Makhtesh Ramon erosional cirque. The obtained results showed the strong effect of soil features of different soil formations on microbial biomass and respiration as well as on the soil free-living nematode communities and its trophic and species composition. The Sorenson-Czenkanowski similarity index indicated significant differences between soil properties as well as between soil biota in observed soil formations. The qCO 2, which is known to increase according to the level of environmental stress, reached maximal values in the sandstone soil formation. The values of ecological indices such as Simpson's dominance index, maturity index and modification and species richness pointed to a specific ecological condition in the studied soil formations dependent on low content of an essential soil matter as soil moisture, organic matter and cations.

Search for pulsation among suspected A-type binaries and the new multiperiodic δ Scuti star HD 217860

We have explored a sample of suspected A-type binaries in a systematic way, both spectroscopically and photometrically. Due to their location in the H-R diagram, indications of pulsation and/or chemical peculiarities among these suspected binary (or multiple) systems may be found. High-resolution spectroscopy obtained with the ELODIE and MUSICOS spectrographs was used in combination with a few nights of differential CCD photometry in order to search for pulsation(s). Of the 32 investigated targets, eight are spectroscopic binaries, one of which is a close binary also showing eclipses, and three have been identified as Delta Scuti pulsators with rapid line-profile variations. Among the latter stars, HD 217860 reveals interesting multiperiodic photometric and spectroscopic variations, with up to eight frequencies common to two large photometric data sets. We suggest that at least one radial overtone mode is excited among the two most dominant frequencies. We furthermore found evidence for a strong modulation of the amplitude(s) and/or the (radial) frequency content of this intriguing Delta Scuti star.

The light variability of the helium strong star HD 37776 as a result of its inhomogeneous elemental surface distribution

We simulate light curves of the helium strong chemically peculiar star HD 37776 assuming that the observed periodic light variations originate as a result of inhomogeneous horizontal distribution of chemical elements on the surface of a rotating star. We show that chemical peculiarity influences the monochromatic radiative flux, mainly due to bound-free processes. Using the model of the distribution of silicon and helium on HD 37776 surface, derived from spectroscopy, we calculate a photometric map of the surface and consequently the uvby light curves of this star. Basically, the predicted light curves agree in shape and amplitude with the observed ones. We conclude that the basic properties of variability of this helium strong chemically peculiar star can be understood in terms of the model of spots with peculiar chemical composition.