Fricke, Klaus J.

[["dc.bibliographiccitation.firstpage","115"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","127"],["dc.bibliographiccitation.volume","429"],["dc.contributor.author","Noeske, K. G."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Cairos, L. M."],["dc.contributor.author","Fricke, K. J."],["dc.date.accessioned","2018-11-07T08:34:49Z"],["dc.date.available","2018-11-07T08:34:49Z"],["dc.date.issued","2005"],["dc.description.abstract","This paper is part of a series of publications which present a systematic study of Blue Compact Dwarf (BCD) Galaxies in the near infrared (NIR). Compared to the visible light, NIR data allow a better separation of the starburst emission from the light distribution of the old stellar low-surface brightness (LSB) host galaxy. We analyze deep NIR broad band images of a sample of 11 BCDs, observed with the Calar Alto 3.6 m telescope. This work enlarges the samples presented in preceding papers of this study (Noeske et al. 2003, A A, 410, 481; Cairos et al. 2003, ApJ, 593, 312) by BCDs of the most common morphological type, displaying a regular elliptical LSB host galaxy. The data presented here allow the detection and quantitative study of the extended stellar LSB host galaxy in all sample BCDs. The NIR surface brightness profiles (SBPs) of the LSB host galaxies agree at large galactocentric radii with those from optical studies, showing also an exponential intensity decrease and compatible scale lengths. Similar to Noeske et al. ( 2003), we find centrally flattening exponential (type V) SBPs of the host galaxy for several BCDs. Such SBPs remain mostly undetected in optical bands, due to the comparatively stronger starburst emission at these wavelengths. We apply a modified exponential distribution to decompose and quantitatively analyze SBPs of LSB hosts with a type V intensity distribution. We present the results of the surface photometry and the decomposition of SBPs, and discuss individual objects with respect to morphological details of their star-forming regions."],["dc.identifier.doi","10.1051/0004-6361:20040221"],["dc.identifier.fs","38257"],["dc.identifier.isi","000225732700016"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9859"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/17913"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","E D P Sciences"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","New insights to the photometric structure of Blue Compact Dwarf Galaxies from deep near-infrared studies - II. The sample of northern BCDs"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","45"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","59"],["dc.bibliographiccitation.volume","457"],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Noeske, K. G."],["dc.contributor.author","Thuan, T. X."],["dc.contributor.author","Fricke, K. J."],["dc.date.accessioned","2019-07-09T11:54:53Z"],["dc.date.available","2019-07-09T11:54:53Z"],["dc.date.issued","2006-10-01"],["dc.description.abstract","Aims. Aiming to find new extremely metal-deficient star-forming galaxies we extracted from the Two-Degree Field Galaxy Redshift Survey (2dFGRS) 100 K Data Release 14 emission-line galaxies with relatively strong [O iii] λ4363 emission. Methods. Spectroscopic and photometric studies of this sample and, in addition, of 7 Tololo and 2 UM galaxies were performed on the basis of observations with the ESO 3.6m telescope. Results. All sample galaxies qualify with respect to their photometric and spectroscopic properties as blue compact dwarf (BCD) galaxies. Additionally, they show a good overlap with a comparison sample of ∼100 well-studied emission-line galaxies on the 12 + log (O/H) vs. log(Ne/O), log(Ar/O) and log(Fe/O) planes. From the analysis of the 2dFGRS subsample we report the discovery of two new extremely metal-deficient BCDs with an oxygen abundance 12 + log (O/H) ≤ 7.6 and of another seven galaxies with 12 + log (O/H) <∼ 7.8. Furthermore, we confirm previous oxygen abundance determinations for the BCDs Tol 1304−353, Tol 2146−391, UM 559 and UM 570 to be 12 + log (O/H) ≤ 7.8."],["dc.identifier.doi","10.1051/0004-6361:20054458"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9875"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/60757"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","New southern blue compact dwarf galaxies in the 2dF Galaxy redshift survey"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","75"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","90"],["dc.bibliographiccitation.volume","407"],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Green, R. F."],["dc.contributor.author","Fricke, K. J."],["dc.contributor.author","Thuan, T. X."],["dc.contributor.author","Noeske, K. G."],["dc.date.accessioned","2018-11-07T10:37:06Z"],["dc.date.available","2018-11-07T10:37:06Z"],["dc.date.issued","2003"],["dc.description.abstract","Spectroscopy and V, I CCD photometry of the dwarf irregular galaxy SBS 1129+576 are presented for the first time. The CCD images reveal a chain of compact H II regions within the elongated low-surface-brightness (LSB) component of the galaxy. Star formation takes place mainly in two high-surface-brightness H II regions. The mean (V-I) colour of the LSB component in the surface brightness interval mu(V) between 23 and 26 mag arcsec(-2) is relatively blue similar to0.56 +/- 0.03 mag, as compared to the (V-I) similar to 0.9-1.0 for the majority of known dwarf irregular and blue compact dwarf (BCD) galaxies. Spectroscopy shows that the galaxy is among the most metal-deficient galaxies with an oxygen abundance 12 + log (O/H) = 7.36 +/- 0.10 in the brightest H II region and 7.48 +/- 0.12 in the second brightest H II region, or 1/36 and 1/28 of the solar value(star), respectively. Hbeta and Halpha emission lines and Hdelta and Hgamma absorption lines are detected in a large part of the LSB component. We use two extinction-insensitive methods based on the equivalent widths of (1) emission and (2) absorption Balmer lines to put constraints on the age of the stellar populations in the galaxy. In addition, we use two extinction-dependent methods based on (3) the spectral energy distribution (SED) and (4) the (V-I) colour. Several scenarios of star formation were explored using all 4 methods. The observed properties of the LSB component can be reproduced by a stellar population forming continuously since 10 Gyr ago, provided that the star formation rate has increased during the last 100 Myr by a factor of 6 to 50 and no extinction is present. However, the observational properties of the LSB component in SBS 1129+576 can be reproduced equally well by continuous star formation which started not earlier than 100 Myr ago and stopped at 5 Myr, if some extinction is assumed. Hence, the ground-based spectroscopic and photometric observations are not sufficient for distinguishing between a young and an old age for SBS 1129+576."],["dc.identifier.doi","10.1051/0004-6361:20030806"],["dc.identifier.isi","000184435000013"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9799"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/45481"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Spectroscopic and photometric studies of low-metallicity star-forming dwarf galaxies - I. SBS 1129+576"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","885"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","893"],["dc.bibliographiccitation.volume","464"],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Fricke, K. J."],["dc.date.accessioned","2019-07-09T11:54:59Z"],["dc.date.available","2019-07-09T11:54:59Z"],["dc.date.issued","2007-03-04"],["dc.description.abstract","Aims.Continuing the systematic determination of the electron temperature of H II regions using the Balmer and/or Paschen discontinuities by Guseva et al. (2006, ApJ, 644, 890) we focus here on 3.6 m ESO telescope observations of a large new sample of 69 H II regions in 45 blue compact dwarf (BCD) galaxies. This data set spans a wide range in metallicity ( $Z_{\\odot}/60 \\la Z \\la Z_{\\odot}/3$) and, combined with the sample of 47 H II regions from Guseva et al. (2006), yields the largest spectroscopic data set ever used to derive the electron temperature in the H+ zone. Methods.In the same way as in Guseva et al. (2006) we have used a Monte Carlo technique to vary free parameters and to calculate a series of model spectral energy distributions (SEDs) for each H II region. The electron temperature in the H+ zones was derived from the best fitting synthetic and observed SEDs in the wavelength range ~3200-5100 Å, which includes the Balmer jump. Results.On the base of the present large spectroscopic sample we find that in hot ($T_{\\rm e}$(H+) $\\ga$ 11 000 K) H II regions the temperature of the O2+ zone, determined from doubly ionised oxygen forbidden lines, does not differ statistically from the temperature of the H+ zone. Thus, we confirm and strengthen the finding by Guseva et al. (2006). We emphasize that due to a number of modelling assumptions and the observational uncertainties for individual objects, only a large, homogeneous sample, as the one used here, can enable a conclusive study of the relation between $T_{\\rm e}$(H+) and $T_{\\rm e}$(O III)."],["dc.identifier.doi","10.1051/0004-6361:20066067"],["dc.identifier.fs","297790"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9939"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/60774"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights","Goescholar"],["dc.rights.access","openAccess"],["dc.rights.uri","https://goedoc.uni-goettingen.de/licenses"],["dc.title","Balmer jump temperature determination in a large sample of low-metallicity HII regions"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","91"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","104"],["dc.bibliographiccitation.volume","407"],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Green, R. F."],["dc.contributor.author","Fricke, K. J."],["dc.contributor.author","Thuan, T. X."],["dc.contributor.author","Noeske, K. G."],["dc.date.accessioned","2018-11-07T10:37:06Z"],["dc.date.available","2018-11-07T10:37:06Z"],["dc.date.issued","2003"],["dc.description.abstract","We present broad-band V and I imaging and long-slit spectroscopy in the optical range lambdalambda3600-7500 Angstrom of the dwarf irregular galaxy HS 1442+4250. The oxygen abundance 12 + log (O/H) = 7.63 +/- 0.02 (Z = Z(circle dot)19)(star) in the brightest H II region of HS 1442+4250 places the galaxy among the most metal-deficient emission-line galaxies. The low metallicity and blue colour (V-I) similar to0.4 mag of the low-surface-brightness (LSB) component make HS 1442+4250 a likely rare young dwarf galaxy candidate. We use four methods to estimate the stellar population age in the LSB component of HS 1442+4250. Different star formation histories are considered. The equivalent widths of hydrogen Halpha and Hbeta emission lines, and of hydrogen Hgamma and Hdelta absorption lines, the spectral energy distribution and the observed (V-I) colours of the LSB regions are reproduced quite well by models with only young and intermediate-age stellar populations. By contrast, the observational data cannot be reproduced by a stellar population formed continuously with a constant star formation rate in the age range from 0 to greater than or equal to 2 Gyr. While a faint old stellar population in HS 1442+4250 with an age greater than or equal to2 Gyr is not excluded, we find no evidence for such a population from the present data."],["dc.identifier.doi","10.1051/0004-6361:20030807"],["dc.identifier.isi","000184435000014"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9800"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/45483"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Spectroscopic and photometric studies of low-metallicity star-forming dwarf galaxies - II. HS 1442+4250"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A149"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","529"],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Stasinska, G."],["dc.contributor.author","Fricke, K. J."],["dc.contributor.author","Henkel, Cornelia"],["dc.contributor.author","Papaderos, P."],["dc.date.accessioned","2018-11-07T08:56:17Z"],["dc.date.available","2018-11-07T08:56:17Z"],["dc.date.issued","2011"],["dc.description.abstract","Context. We present deep spectroscopy of a large sample of low-metallicity emission-line galaxies. Aims. The main goal of this study is to derive element abundances in these low-metallicity galaxies. Methods. We analyze 121 VLT spectra of H II regions in 46 low-metallicity emission-line galaxies. Of these spectra 83 are archival VLT/FORS1 + UVES spectra of H II regions in 31 low-metallicity emission-line galaxies that are studied for the first time with standard direct methods to determine the electron temperatures, the electron number densities, and the chemical abundances. Results. The oxygen abundance of the sample lies in the range 12 + log O/H = 7.2-8.4. We confirm previous findings that Ne/O increases with increasing oxygen abundance, likely because of a higher depletion of oxygen in higher-metallicity galaxies. The Fe/O ratio decreases from roughly solar at the lowest metallicities to about one tenth of solar, indicating that the degree of depletion of iron into dust grains depends on metallicity. The N/O ratio in extremely low-metallicity galaxies with 12 + log O/H < 7.5 shows a slight increase with decreasing oxygen abundance, which could be the signature of enhanced production of primary nitrogen by rapidly rotating stars at low metallicity. We present the first empirical relation between the electron temperature derived from [S III]lambda 6312/lambda 9069 or [N II]lambda 5755/lambda 6583 and the one derived from [O III]lambda 4363/lambda(4959 + 5007) in low-metallicity galaxies. We also present an empirical relation between t(e) derived from [O II]lambda 3727/(lambda 7320 + lambda 7330) or [S II]lambda 4068/(lambda 6717 + lambda 6730) and [O III]lambda 4363/lambda(4959 + 5007). The electron number densities N-e(Cl III) and N-e(Ar IV) were derived in a number of objects and are found to be higher than N-e(O II) and N-e(S II). This has potential implications for the derivation of the pregalactic helium abundance. In a number of objects, the abundances of C++ and O++ could be derived from recombination lines. Our study confirms the discrepancy between abundances found from recombination lines (RLs) and collisionally excited lines (CELs) and that C/O increases with O/H."],["dc.identifier.doi","10.1051/0004-6361/201016291"],["dc.identifier.fs","590499"],["dc.identifier.isi","000294240700024"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/8604"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/23104"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","VLT spectroscopy of low-metallicity emission-line galaxies: abundance patterns and abundance discrepancies"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","519"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","528"],["dc.bibliographiccitation.volume","421"],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Noeske, K. G."],["dc.contributor.author","Fricke, K. J."],["dc.date.accessioned","2018-11-07T10:47:20Z"],["dc.date.available","2018-11-07T10:47:20Z"],["dc.date.issued","2004"],["dc.description.abstract","We present a ground-based optical spectroscopic and HST U, V, I photometric study of the blue compact dwarf (BCD) galaxy Pox 186. It is found that the emission of the low-surface brightness (LSB) component in Pox 186 at radii less than or similar to3\" (5270 pc in linear scale) is mainly gaseous in origin. We detect Ha emission out to radii as large as 6\". At radii greater than or similar to3\" the light of the LSB component is contaminated by the emission of background galaxies complicating the study of the outermost regions. The surface brightness distribution in the LSB component can be approximated by an exponential law with a scale length alpha less than or similar to 120 pc. This places Pox 186 among the most compact dwarf galaxies known. The derived a is likely to be an upper limit to the scale length of the LSB component because of the strong contribution of the gaseous emission. The oxygen abundance in the bright H II region derived from the 4.5 m Multiple Mirror Telescope (MMT) and 3.6 m ESO telescope spectra are 12 + log (O/H) = 7.76 +/- 0.02 and 7.74 +/- 0.01 (-Z(circle dot)/15) , respectively, in accordance with previous determinations. The helium mass fractions found in this region are Y = 0.248 +/- 0.009 (MMT) and Y = 0.248 +/- 0.004 (3.6 m) suggesting a high primordial helium abundance."],["dc.identifier.doi","10.1051/0004-6361:20035949"],["dc.identifier.fs","21429"],["dc.identifier.isi","000222897700017"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9820"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/47940"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","E D P Sciences"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Pox 186: An ultracompact galaxy with dominant ionized gas emission"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","113"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","129"],["dc.bibliographiccitation.volume","491"],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Fricke, K. J."],["dc.date.accessioned","2018-11-07T11:09:17Z"],["dc.date.available","2018-11-07T11:09:17Z"],["dc.date.issued","2008"],["dc.description.abstract","Context. Extremely metal-deficient [12 + log(O/H) less than or similar to 7.6] emission-line galaxies in the nearby universe are invaluable laboratories of extragalactic astronomy and observational cosmology since they allow us to study collective star formation and the evolution of galaxies under chemical conditions approaching those in distant protogalactic systems. However, despite intensive searches over the last three decades, nearby star-forming (SF) galaxies with strongly subsolar metallicity remain extremely scarce. Aims. We searched the Sloan Digital Sky Survey (SDSS) and the Six-Degree Field Galaxy Redshift Survey (6dFGRS) for promising low-metallicity candidates using a variety of spectroscopic criteria. Methods. We present long-slit spectroscopy with the 3.6 m ESO telescope of eight HII regions in seven emission-line dwarf galaxies, selected from the Data Release 4 of SDSS ( six galaxies) and from 6dFGRS ( one galaxy). In addition, we use SDSS imaging data to investigate the photometric structure of the sample galaxies. Results. From the 3.6 m telescope spectra, we determine the oxygen abundance of these systems to be 7.3 less than or similar to 12 + log(O/H) less than or similar to 7.6, placing them among the most metal-poor star-forming galaxies ever discovered. Our photometric analysis reveals a moderately blue, stellar host galaxy in all sample galaxies. Conclusions. The detection of a stellar host in all galaxies studied here and all previously studied extremely metal-deficient SF galaxies implies that they are unlikely to be forming their first generation of stars. With regard to the structural properties of their host galaxy, we demonstrate that these systems are indistinguishable from blue compact dwarf (BCD) galaxies. However, in contrast to the majority (> 90%) of BCDs that are characterised by red elliptical host galaxies, extremely metal-poor SF dwarfs (hereafter XBCDs) reveal moderately blue and irregular hosts. This is consistent with a young evolutionary status and in the framework of standard star formation histories implies that several XBCDs formed most of their stellar mass in the past similar to 2 Gyr. A large fraction of XBCDs reveal a cometary morphology due to the presence of intense SF activity at one edge of an elongated host galaxy with a gradually decreasing surface brightness towards its antipodal end."],["dc.identifier.doi","10.1051/0004-6361:200810028"],["dc.identifier.isi","000260559700010"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9950"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/52973"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Extremely metal-poor star-forming galaxies New detections and general morphological and photometric properties"],["dc.type","review"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","61"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","U95"],["dc.bibliographiccitation.volume","503"],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Fricke, K. J."],["dc.contributor.author","Papaderos, P."],["dc.date.accessioned","2018-11-07T11:25:51Z"],["dc.date.available","2018-11-07T11:25:51Z"],["dc.date.issued","2009"],["dc.description.abstract","Context. We present deep archival VLT/FORS1+UVES spectroscopic observations of the system of two blue compact dwarf (BCD) galaxies SBS 0335-052E and SBS 0335-052W. Aims. Our aim is to derive element abundances in different H II regions of this unique system of galaxies and to study spatial abundance variations. Methods. The electron temperature T(e) (O III) in all H II regions, except for one, is derived from the [O III] lambda 4363/(lambda 4959+lambda 5007) flux ratio. We determine ionic abundances of helium, nitrogen, oxygen, neon, sulfur, chlorine, argon and iron. The empirical relations for ionization correction factors are used to derive total abundances of these elements. Results. The oxygen abundance in the brighter eastern galaxy varies in the range 7.11 to 7.32 in different H II regions supporting previous findings and suggesting the presence of oxygen abundance variations on spatial scales of similar to 1-2 kpc. Good seeing during FORS observations allowed us to extract spectra of four H II regions in SBS 0335-052W. The oxygen abundance in the brightest region No. 1 of SBS 0335-052W is 7.22 +/- 0.07, consistent with previous determinations. Three other H II regions are much more metal-poor with an unprecedently low oxygen abundance of 12 + log O/H = 7.01 +/- 0.07 (region No. 2), 6.98 +/- 0.06 (region No. 3), and 6.86 +/- 0.14 (region No. 4). These are the lowest oxygen abundances ever derived in emission-line galaxies, supporting earlier conclusions that SBS 0335-052W is the lowest-metallicity emission-line galaxy known. Helium abundances derived for the brightest H II regions of both galaxies are mutually consistent. We derive weighted mean He mass fractions of 0.2485 +/- 0.0012 and 0.2514 +/- 0.0012 for two different sets of He I emissivities. The ratios of neon and sulfur to oxygen abundance are similar to the respective ratios obtained for other emission-line galaxies. On the other hand, the chlorine-to-oxygen abundance ratio in SBS 0335-052E is lower, while the argon-to-oxygen abundance ratio is higher than those in other low-metallicity galaxies. The Fe/O abundance ratios in different regions of SBS 0335-052E are among the highest for emission-line galaxies implying that iron is almost entirely not depleted onto dust grains despite dust being detected in this galaxy in earlier ISO and Spitzer observations. The N/O abundance ratio in both galaxies is slightly higher than that derived for other BCDs with 12 + logO/H < 7.6. This implies that the N/O in extremely metal-deficient galaxies could increase with decreasing metallicity."],["dc.identifier.doi","10.1051/0004-6361/200911965"],["dc.identifier.fs","573778"],["dc.identifier.isi","000269150300010"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9699"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/56721"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","SBS 0335-052E+W: deep VLT/FORS plus UVES spectroscopy of the pair of the lowest-metallicity blue compact dwarf galaxies"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","756"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","776"],["dc.bibliographiccitation.volume","378"],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Chaffee, F. H."],["dc.contributor.author","Foltz, C. B."],["dc.contributor.author","Green, R. F."],["dc.contributor.author","Thuan, T. X."],["dc.contributor.author","Fricke, K. J."],["dc.contributor.author","Noeske, K. G."],["dc.date.accessioned","2018-11-07T11:25:54Z"],["dc.date.available","2018-11-07T11:25:54Z"],["dc.date.issued","2001"],["dc.description.abstract","We present the results of spectrophotometry and V, R, I, H alpha CCD photometry of the blue compact dwarf (BCD) galaxy SBS 0940+544. Broad-band images taken with the 2.1 m KPNO and 1.23 m Calar Alto telescopes reveal a compact high-surface-brightness H II region with ongoing star formation, located at the northwestern tip of the elongated low surface brightness (LSB) main body of the BCD. Very faint, patchy emission along the main body is seen in the H alpha image. High signal-to-noise 4.5 m Multiple Mirror Telescope (MMT) and 10 m Keck II telescope dagger long-slit spectroscopy of SBS 0940+544 is used to derive element abundances of the ionized gas in the brightest H II region and to study the stellar population in the host galaxy. The oxygen abundance in the brightest region with strong emission lines is 12 + log(O/H) = 7.46-7.50, or 1/29-1/26 solar, in agreement with earlier determinations and among the lowest for BCDs. H beta and H alpha emission lines and H delta and H gamma absorption lines are detected in a large part of the main body. Three methods are used to put constraints on the age of the stellar population at different positions along the major axis. They are based on (a) the equivalent widths of the emission lines, (b) the equivalent widths of the absorption lines and (c) the spectral energy distributions (SED). Several scenarios of star formation have been considered. We find that models with single instantaneous bursts cannot reproduce the observed SEDs, implying that star formation in the main body of SBS 0940+544 was continuous. The observed properties in the main body can be reproduced by a continuous star formation process which started not earlier than 100 Myr ago, if a small extinction is assumed. However, the observations can be reproduced equally well by a stellar population forming continuously since 10 Gyr, if the star formation rate has increased during last 100 Myr in the main body of SBS 0940+544 by at least a factor of five. We also investigate the age of the reddest southern region of the main body, where no absorption and emission lines are detected. On the assumption of zero extinction in this faint region, the observed spectrum can be fitted by a theoretical SED of a stellar population continuously formed with a constant star formation rate between 100 Myr and 10 Gyr ago. If, however, a small extinction of C(H beta) similar to 0.1 is present in this region then the observed spectrum can be fitted by a theoretical SED of a stellar population continuously formed between 100 Myr and 1 Gyr ago with a constant star formation rate. However, the poor signal-to-noise ratio of the spectrum and large photometric errors preclude reliable determination of the age of the southern region. In summary, we find no compelling evidence which favors either a young or an old age of SBS 0940+544."],["dc.identifier.doi","10.1051/0004-6361:20011195"],["dc.identifier.isi","000171897200007"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9715"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/56731"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","The evolutionary status of the low-metallicity blue compact dwarf galaxy SBS 0940+544"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]