arXiv subjects

E. Paunzen

Publications and source records attributed to E. Paunzen.

At least 91 records · Page 5Linked to original sources

arXiv2014

The first Delta a observations of three globular clusters

Globular clusters are main astrophysical laboratories to test and modify evolutionary models. Thought to be rather homogeneous in their local elemental Distribution of members, results suggest a wide variety of chemical peculiarities. Besides different main sequences, believed to be caused by different helium abundances, peculiarities of blue horizontal-branch stars and on the red giant branch were found. This whole zoo of peculiar objects has to be explained in the context of stellar formation and evolution. The tool of Delta a photometry is employed in order to detect peculiar stars in the whole spectral range. This three filter narrow band system measures the flux distribution in the region from 4900 to 5600A in order to find any peculiarities around 5200A. It is highly efficient to detect classical chemically peculiar stars of the upper main sequence, Be/Ae, shell and metal-weak objects in the Milky Way and Magellanic Clouds. We present Delta a photometry of 2266 stars from 109 individual frames for three globular Clusters (NGC 104, NGC 6205, and NGC 7099). A comparison with published abundances, for three horizontal-branch stars, only, yield an excellent agreement. According to the 3 sigma detection limit of each globular cluster, about 3% of the stars lie in abnormal regions in the diagnostic diagrams. The first observations of three widely different aggregates give very promising results, which will serve as a solid basis for follow-up observations including photometric as well as spectroscopic studies.

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arXiv2014

Investigating the possible connection between lambda Bootis stars and intermediate Population II type stars

The lambda Bootis (LB) stars are located at the upper main sequence of the H-R diagram and exhibit a peculiar abundance pattern. The light elements (C, N, O, and S) present solar abundances whereas all other elements are moderately to strongly underabundant. It has not yet been determined whether that abundance pattern is intrinsic, or is restricted to the stellar surface. If we follow the hypothesis that the LB stars are intrinsically metal-weak, then there should be a connection with the intermediate Population II and F-weak objects. Such a possible affinity has not been previously investigated. We present detailed elemental abundances, including those of the light elements carbon and oxygen, for 38 bright intermediate Population II and F-weak objects. In addition, we investigate the kinematic characteristics of the groups. From photometric, spectroscopic, and kinematic data, there is no distinction between the intermediate Population II and F-weak type stars. We therefore conclude that the two groups are identical. However, it is possible to distinguish the LB stars from the intermediate Population II stars on the basis of elemental abundances, though not in terms of their kinematics. The LB stars seem to be distinct from the intermediate Population II group. Further asteroseismologic investigations and analyses of spectroscopic binary systems are needed to strengthen this conclusion.

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arXiv2014

A probable pre-main sequence chemically peculiar star in the open cluster Stock 16

We used the Ultraviolet and Visual Echelle Spectrograph of the ESO-Very Large Telescope to obtain a high resolution and high signal-to-noise ratio spectrum of Stock 16-12, an early-type star which previous Delta-a photometric observations suggest being a chemically peculiar (CP) star. We used spectral synthesis to perform a detailed abundance analysis obtaining an effective temperature of 8400 +/- 400 K, a surface gravity of 4.1 +/- 0.4, a microturbulence velocity of 3.4 +0.7/-0.3 km/s, and a projected rotational velocity of 68 +/- 4 km/s. We provide photometric and spectroscopic evidence showing the star is most likely a member of the young Stock 16 open cluster (age 3-8 Myr). The probable cluster membership, the star's position in the Hertzsprung-Russell diagram, and the found infrared excess strongly suggest the star is still in the pre-main-sequence (PMS) phase. We used PMS evolutionary tracks to determine the stellar mass, which ranges between 1.95 and 2.3 Msun, depending upon the adopted spectroscopic or photometric data results. Similarly, we obtained a stellar age ranging between 4 and 6 Myr, in agreement with that of the cluster. Because the star's chemical abundance pattern resembles well that known of main sequence CP metallic line (Am) stars, the object sets important constraints to the diffusion theory. Additional spectroscopic and spectropolarimetric data allowed us to conclude that the object is probably a single non-magnetic star.

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arXiv2014

HD 54272, a classical lambda Bootis star and gamma Doradus pulsator

We detect the second known lambda Bootis star (HD 54272) which exhibits gamma Doradus-type pulsations. The star was formerly misidentified as a RR Lyrae variable. The lambda Bootis stars are a small group (only 2 per cent) of late B to early F-type, Population I stars which show moderate to extreme (up to a factor 100) surface underabundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O, and S). The photometric data from the Wide Angle Search for Planets (WASP) and All Sky Automated Survey (ASAS) projects were analysed. They have an overlapping time base of 1566 d and 2545 d, respectively. Six statistically significant peaks were identified (f1 = 1.410 116 c/d, f2 = 1.283 986 c/d, f3 = 1.293 210 c/d, f4 = 1.536 662 c/d, f5 = 1.157 22 c/d and f6 = 0.226 57 c/d). The spacing between f1 and f2, f1 and f4, f5 and f2 is almost identical. Since the daily aliasing is very strong, the interpretation of frequency spectra is somewhat ambiguous. From spectroscopic data, we deduce a high rotational velocity (250+-25 km/s) and a metal deficiency of about -0.8 to -1.1 dex compared to the Sun. A comparison with the similar star, HR 8799, results in analogous pulsational characteristics but widely different astrophysical parameters. Since both are lambda Bootis-type stars, the main mechanism of this phenomenon, selective accretion, may severely influence gamma Doradus-type pulsations.

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arXiv2014

Photoelectric search for peculiar stars in open clusters. XV. Feinstein 1, NGC 2168, NGC 2323, NGC 2437, NGC 2547, NGC 4103, NGC 6025, NGC 6633, Stock 2, and Trumpler 2

The chemically peculiar (CP) stars of the upper main sequence are mainly characterized by strong overabundances of heavy elements. Two subgroups (CP2 and CP4) have strong local magnetic fields which make them interesting targets for astrophysical studies. This star group, in general, is often used for the analysis of stellar formation and evolution in the context of diffusion as well as meridional circulation. In continuation of a long term study of CP stars (initiated in the 1980ies), we present new results based on photoelectric measurements for ten open clusters that are, with one exception, younger than 235Myr. Observations in star clusters are favourable because they represent samples of stars of constant age and homogeneous chemical composition. The very efficient tool of Delta a photometry was applied. It samples the flux depression at 5200A typically for CP stars. In addition, it is able to trace emission line Be/Ae and lambda Bootis stars. Virtually all CP2 and CP4 stars can be detected via this tool. For all targets in the cluster areas, we performed a kinematic membership analysis. We obtained new photoelectric Delta a photometry of 304 stars from which 207 objects have a membership probability higher than 50%. Our search for chemically peculiar objects results in fifteen detections. The stars have masses between 1.7 M(Sun) and 7.7 M(Sun) and are between the zero- and terminal-age-main-sequence. We discuss the published spectral classifications in the light of our Delta a photometry and identify several misclassified CP stars. We are also able to establish and support the nature of known bona fide CP candidates. The new and confirmed CP stars are interesting targets for spectroscopic follow-up observations to put constraints on the formation and evolution of CP stars.

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arXiv2014

Spectrophotometric analysis of the 5200A region for peculiar and normal stars

Many chemically peculiar (CP) stars, especially the magnetic CP2 stars, show a flux depression at 5200A. The "Delta a" photometric System takes advantage of this characteristic to detect these objects in an efficient way. In addition, it is capable of finding metal-weak, emission-type, and shell-type objects of the upper main sequence. To compare available observations and to detect new peculiar objects, we used a spectrophotometric catalogue consisting of 1159 stars. From this catalogue, we selected 1067 objects to synthesize three different "a" indices to find the most efficient one for further observations. In addition, we extended the analysis to stars cooler than F5. We employed classical "Delta a" photometry described by Maitzen, using simulated filter curves, the spectrophotometric "Delta a" index by Adelman, and a modified index. During this investigation magnetic chemically peculiar stars could be confirmed using the data of the catalogue and in addition we noticed an unknown behavior for red stars in "Delta a", becoming independent of B-V. Even though the accuracy of the spectrophotometry used for this investigation is significantly lower than the photometric "Delta a" measurements, we are able to confirm peculiarity for most of the known CP2 stars above a certain limit of "Delta a". We investigated 631 stars hotter than spectral type F5 to find additional that are not yet identified peculiar objects. We find that for very low mass stars (M0), the "a" index is independent of the colour (effective temperature). The "Delta a" photometric system is very closely correlated with the effective temperature over a wide range of the main sequence. It is able to detect any kind of peculiarity connected to the 5200A region. Especially for low-mass stars, this opens up a new possibility of detecting peculiar objects in an efficient way.

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arXiv2013

On the metallicity of open clusters II. Spectroscopy

In a series of three papers, we investigate the current status of published metallicities for open clusters that were derived from a variety of photometric and spectroscopic methods. The current article focuses on spectroscopic methods. The aim is to compile a comprehensive set of clusters with the most reliable metallicities from high-resolution spectroscopic studies. This set of metallicities will be the basis for a calibration of metallicities from different methods. The literature was searched for [Fe/H] estimates of individual member stars of open clusters based on the analysis of high-resolution spectra. For comparison, we also compiled [Fe/H] estimates based on spectra with low and intermediate resolution. At medium and high resolution, we found that differences in the analysis methods have a stronger effect on metallicity than quality differences in the observations. We retained only highly probable cluster members and introduced a restriction on atmospheric parameters. We combined 641 individual metallicity values for 458 stars in 78 open clusters from 86 publications to form our final set of high-quality cluster metallicities. The photometric metallicities discussed in the first paper of this series are systematically lower than the spectroscopic ones by about 0.1 dex, and the differences show a scatter of about 0.2 dex. In a preliminary comparison of our spectroscopic sample with models of Galactic chemical evolution, none of the models predicts the observed radial metallicity gradient. Photometric metallicities show a large intrinsic dispersion, while the more accurate spectroscopic sample presented in this paper comprises fewer than half the number of clusters. Only a sophisticated combination of all available photometric and spectroscopic data will allow us to trace the metallicity distribution in the Galactic disk on a local and global scale.

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arXiv2013

The (non-)variability of magnetic chemically peculiar candidates in the Large Magellanic Cloud

The galactic magnetic chemically peculiar (mCP) stars of the upper main sequence are well known as periodic spectral and light variables. The observed variability is obviously caused by the uneven distribution of overabundant chemical elements on the surfaces of rigidly rotating stars. The mechanism causing the clustering of some chemical elements into disparate structures on mCP stars has not been fully understood up to now. The observations of light changes of mCP candidates recently revealed in the nearby Large Magellanic Cloud (LMC) should provide us with information about their rotational periods and about the distribution of optically active elements on mCP stars born in other galaxies. We queried for photometry at the Optical Gravitational Lensing Experiment (OGLE)-III survey of published mCP candidates selected because of the presence of the characteristic 5200A flux depression. In total, the intersection of both sources resulted in twelve stars. We performed our own and standard periodogram time series analyses of all available data. The final results are, amongst others, the frequency of the maximum peak and the bootstrap probability of its reality. We detected that only two mCP candidates, 190.1 1581 and 190.1 15527, may show some weak rotationally modulated light variations with periods of 1.23 and 0.49 days; however, the 49% and 32% probabilities of their reality are not very satisfying. The variability of the other 10 mCP candidates is too low to be detectable by their V and I OGLE photometry. The relatively low amplitude variability of the studied LMC mCP candidates sample can be explained by the absence of photometric spots of overabundant optically active chemical elements. The unexpected LMC mCPs behaviour is probably caused by different conditions during the star formation in the LMC and the Galaxy.

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arXiv2013

Towards a photometric metallicity scale for open clusters

Open clusters are a useful tool when investigating several topics connected with stellar evolution; for example the age or distance can be more accurately determined than for field stars. However, one important parameter, the metallicity, is only known for a marginal percentage of open clusters. We aim at a consistent set of parameters for the open clusters investigated in our photometric Delta-a survey of chemically peculiar stars. Special attention is paid to expanding our knowledge of cluster metallicities and verifying their scale. Making use of a previously developed method based on normalised evolutionary grids and photometric data, the distance, age, reddening, and metallicity of open clusters were derived. To transform photometric measurements into effective temperatures to use as input for our method, a set of temperature calibrations for the most commonly used colour indices and photometric systems was compiled. We analysed 58 open clusters in total. Our derived metallicity values were in excellent agreement with about 30 spectroscopically studied targets. The mean value of the absolute deviations was found to be 0.03 dex, with no noticeable offset or gradient. The method was also applied using recent evolutionary models based on the currently accepted lower solar abundance value Z=0.014. No significant differences were found compared to grids using the former adopted solar value Z=0.02. Furthermore, some divergent photometric datasets were identified and discussed. The method provides an accurate way of obtaining properly scaled metallicity values for open clusters. In light of present and future homogeneous photometric sky surveys, the sample of stellar clusters can be extended to the outskirts of the Milky Way, where spectroscopic studies are almost impossible. This will help for determining galactic metallicity gradients in more detail.

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arXiv2012

A photometric study of chemically peculiar stars with the STEREO satellites. II. Non-magnetic chemically peculiar stars

We have analysed the photometric data obtained with the STEREO spacecraft for 558 non-magnetic chemically peculiar (CP) stars to search for rotational and pulsational variability. Applying the Lomb-Scargle and the phase dispersion minimisation methods, we have detected photometric variability for 44 objects from which 35 were previously unknown. The new objects are all bright stars on the Ecliptic Plane (magnitude range 4.7 < V < 11.7) and will therefore be of great interest to studies of stellar structure and evolution. In particular, several show multiple signals consistent with hybrid delta Scuti and gamma Doradus pulsation, with different periodicities allowing very different regions of the stellar interior to be studied. There are two subgroups of stars in our sample: the cool metallic line Am (CP1) and the hot HgMn (CP3) stars. These objects fall well inside the classical instability strip where delta Scuti, gamma Doradus and slowly pulsating B-type stars are located. We also expect to find periods correlated to the orbital period for CP1 objects as they are mostly members of binary systems. For CP3 stars, rotationally-induced variability is still a matter of debate. Although surface spots were detected, they are believed to produce only marginal photometric amplitudes. So, periods from several hours to a few days were expected for these two star groups. The remaining 514 stars are likely to be constant in the investigated range from 0.1 to 10 days. In some cases, the presence of blending or systematic effects prevented us from detecting any reliable variability and in those cases we classified the star as constant. Finally, we have calibrated the variable stars in terms of the effective temperature and luminosity in order to estimate masses and ages. For this purpose we used specifically developed calibrations for CP stars and, when available, HIPPARCOS parallaxes.

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arXiv2011

HD 210111: a new lambda Bootis type SB system

The small group of lambda Bootis stars comprises late B to early F-type stars, with moderate to extreme (up to a factor 100) surface underabundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O, and S). The main mechanisms responsible for this phenomenon are atmospheric diffusion, meridional mixing and accretion of material from their surroundings. Especially spectroscopic binary (SB) systems with lambda Bootis type components are very important to investigate the evolutionary status and accretion process in more details. For HD 210111, also delta Scuti type pulsation was found which gives the opportunity to use the tools of asteroseismology for further investigations. The latter could result in strict constraints for the amount of diffusion for this star. Together with models for the accretion and its source this provides a unique opportunity to shed more light on these important processes. We present classification and high resolution spectra for HD 210111. A detailed investigation of the most likely combinations of single star components was performed. For this, composite spectra with different stellar astrophysical parameters were calculated and compared to the observations to find the best fitting combination. HD 210111 comprises two equal (within the estimated errors) stars with T(eff)=7400K, logg=3.8dex, [M/H]=-1.0dex and vsini=30km/s. This result is in line with other strict observational facts published so far for this object. It is only the third detailed investigated lambda Bootis type SB system, but the first one with a known IR-excess.

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arXiv2011

A photometric study of chemically peculiar stars with the STEREO satellites. I. Magnetic chemically peculiar stars

About 10% of upper main sequence stars are characterised by the presence of chemical peculiarities, often found together with a structured magnetic field. The atmospheres of most of those chemically peculiar stars present surface spots, leading to photometric variability caused by rotational modulation. The study of the light curves of those stars therefore, permits a precise measurement of their rotational period, which is important to study stellar evolution and to plan further detailed observations. We analysed the light curves of 1028 chemically peculiar stars obtained with the STEREO spacecraft. We present here the results obtained for the 337 magnetic chemically peculiar stars in our sample. Thanks to the cadence and stability of the photometry, STEREO data are perfectly suitable to study variability signals with a periodicity typical of magnetic chemically peculiar stars. Using a matched filter algorithm and then two different period searching algorithms, we compiled a list of 82 magnetic chemically peculiar stars for which we measured a reliable rotational period; for 48 of them this is the first measurement of their rotational period. The remaining 255 stars are likely to be constant, although we cannot exclude the presence of long period variability. In some cases, the presence of blending or systematic effects prevented us from detecting any reliable variability and in those cases we classified the star as constant. For each star we classified as variable, we determined temperature, luminosity, mass and fractional age, but the limited statistics, biased towards the shorter periods, prevented us from finding any evolutionary trend of the rotational period. For a few stars, the comparison between their projected rotational velocity and equatorial velocity let us believe that their real rotational period might be longer than that found here and previously obtained.

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arXiv2010

A photometric long-term study of CP stars in open clusters

Photometric variability of chemically peculiar (CP) stars of the upper main sequence is closely connected to their local stellar magnetic field and their rotational period. Long term investigations, as presented here, help us to identify possible stellar cycles (as in the Sun). Furthermore, these data provide a basis for detailed surface mapping techniques. Photoelectric Stroemgren uvby time series for 27 CP stars within the boundaries of open clusters are presented. In addition, Hipparcos photometric data (from 1989 to 1993) are used for our analysis. Our observations cover a time period of about six years (1986 to 1992) with typically fifteen measurements for each objects. These observations help us to determine the rotational periods of these objects. A standard reduction procedure was applied to the data. When possible, we merged our data sets with already published ones to obtain a more significant result. A detailed time series analysis was performed, involving five different methods to minimize spurious detections. We established, for the first time, variability for fourteen CP stars. For additional two stars, a merging of already published data sets, resulted in more precise periods, whereas for six objects, the published periods could be confirmed. Last, but not least, no significant variations were found for five stars. Apart from six stars, all targets seem to be members of their host open clusters.

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arXiv2010

The first spectroscopic verification of an extragalactic classical chemically peculiar star

We present the first spectroscopic verification of a bona fide chemically peculiar (CP) star in the Large Magellanic Cloud. CP stars reside on the upper main sequence and are characterized by strong global stellar magnetic fields with a predominant dipole component oriented at random with respect to the stellar rotation axis and displaced from the star's centre. Overabundances with respect to the Sun for heavy elements such as silicon, chromium, strontium and europium are also a common phenomenon. These objects are excellent astrophysical laboratories by which to investigate many of the processes connected with star formation and evolution. Several studies comparing the incidence of CP stars in the Large Magellanic Cloud with that of the Milky Way have been published. These investigations are based on the photometric detection of CP stars via the Delta a system which has been tested and calibrated for objects in the Milky Way. From our spectroscopic observations made at Las Campanas Observatory, we are able to confirm one classical B8 Si star among the photometric sample, as well as one early B-type emission-line star which was also initially detected by its significantly deviating Delta a value. We conclude that classical extragalactic CP stars do exist and that the photometric Delta a system is able to detect them in an efficient way.

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arXiv2010

On the metallicity of open clusters I. Photometry

Metallicity is one of four free parameters typically considered when fitting isochrones to the cluster sequence. Unfortunately, this parameter is often ignored or assumed to be solar in most papers. Hence an unknown bias is introduced in the estimation of the other three cluster parameters (age, reddening and distance). Furthermore, studying the metallicity of open clusters allows us not only to derive the Galactic abundance gradient on a global scale, but also to trace the local solar environment in more detail. In a series of three papers, we investigate the current status of published metallicities for open clusters from widely different photometric and spectroscopic methods. A detailed comparison of the results allows us to establish more reliable photometric calibrations and corrections for isochrone fitting techniques. Well established databases such as WEBDA help us to perform a homogeneous analysis of available measurements for a significant number of open clusters. The literature was searched for [Fe/H] estimates on the basis of photometric calibrations in any available filter system. On the basis of results published by Tadross, we demonstrate the caveats of the calibration choice and its possible impact. In total, we find 406 individual metallicity values for 188 open clusters within 64 publications. The values were, finally, unweightedly averaged. Our final sample includes [Fe/H] values for 188 open clusters. Tracing the solar environment within 4000x4000 pc**2 we identify a patchy metallicity distribution as an extension to the Local Bubble that significantly influences the estimation of the Galactic metallicity gradient, even on a global scale. In addition, further investigations of more distant open clusters are clearly needed to obtain a more profound picture at Galactocentric distances beyond 10 000 pc.

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arXiv2010

HR 7355 - another rapidly braking He-strong CP star?

Strong meridional mixing induced by rapid rotation is one reason why all hot main-sequence stars are not chemically peculiar. However, the finding that the He-strong CP star HR 7355 is a rapid rotator complicates this concept. Our goal is to explain the observed behaviour of HR 7355 based on period analysis of all available photometry. Over two years, we acquired 114 new BV observations of HR 7355 at observatories in Arizona, U.S.A and Cape Town, South Africa. We performed period analyses of the new observations along with new analyses of 732 archival measurements from the Hipparcos and ASAS projects. We find that the light curves of HR 7355 in various filters are quite similar, with amplitudes 0.035(4), 0.036(4), and 0.038(3) mag in B, Hp and V, respectively. The light curves are double-peaked, with unevenly deep minima. We substantially refine the rotational period to be P=0.5214410(4) d, indicating that HR 7355 is the most rapidly rotating CP star known. Our period analyses reveal a possible lengthening of the rotational period with dP/dt/P = 2.4(8)x 10^-6/yr. We conclude that the shape and amplitude of HR 7355 light curves are typical of magnetic He-strong CP stars, for which light variations are the result of photospheric spots on the surface of a rotating star. We hypothesise that the light variations are caused mainly by an uneven distribution of overabundant helium on the star's surface. We briefly describe and discuss the cause of the rapid rotational braking of the star.

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arXiv2009

CCD BV and 2MASS photometric study of the open cluster NGC 1513

We present CCD BV and JHK$_{s}$ 2MASS photometric data for the open cluster NGC 1513. We observed 609 stars in the direction of the cluster up to a limiting magnitude of $V\sim19$ mag. The star count method shows that the centre of the cluster lies at $α_{2000}=04^{h}09^{m}36^{s}$, $δ_{2000}=49^{\circ}28^{'}43^{''}$ and its angular size is $r=10$ arcmin. The optical and near-infrared two-colour diagrams reveal the colour excesses in the direction of the cluster as $E(B-V)=0.68\pm0.06$, $E(J-H)=0.21\pm0.02$ and $E(J-K_{s})=0.33\pm0.04$ mag. These results are consistent with normal interstellar extinction values. Optical and near-infrared Zero Age Main-Sequences (ZAMS) provided an average distance modulus of $(m-M)_{0}=10.80\pm0.13$ mag, which can be translated into a distance of $1440\pm80$ pc. Finally, using Padova isochrones we determined the metallicity and age of the cluster as $Z=0.015\pm 0.004$ ($[M/H]=-0.10 \pm 0.10$ dex) and $\log (t/yr) = 8.40\pm0.04$, respectively.

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arXiv2008

Chemically peculiar stars and their temperature calibration

The determination of effective temperature for chemically peculiar (CP) stars by means of photometry is a sophisticated task due to their abnormal colours. Standard calibrations for normal stars lead to erroneous results and, in most cases corrections are necessary. In order to specify appropriate corrections, direct temperature determinations for 176 objects of the different subgroups were collected from the literature. This much larger sample than in previous studies therefore allows a more accurate investigation, mostly based on average temperatures. For the three main photometric systems (UBV, Geneva, Stromgren uvbybeta), methods to determine effective temperature are presented together with a comparison with former results. Based on the compiled data we provide evidence that He (CP4) objects also need a considerable correction, not noticed in former investigations due to their small number. Additionally, a new relation for the bolometric correction and the capability of standard calibrations to deduce interstellar reddening for magnetic CP stars are shown.

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