Observations were carried out on 2005 June 30 and July 6 at the 3.5-m telescope at Calar Alto Obs... more Observations were carried out on 2005 June 30 and July 6 at the 3.5-m telescope at Calar Alto Observatory with the Potsdam MultiAperture Spectrograph, PMAS, in the PPAK mode. We obtained publicly available HST/ACS images of the cluster in the F475W, F555W, F625W, F775W and F850LP bands from the HST archive.
We present new measurements of central line-strength indices (namely Mg2, 〈Fe〉, and Hβ) and gradi... more We present new measurements of central line-strength indices (namely Mg2, 〈Fe〉, and Hβ) and gradients for a sample of 6 bright spheroidal galaxies (Sph’s) in the Virgo cluster. Comparison with similar measurements for elliptical galaxies (E’s), galactic globular clusters (GGC’s), and stellar population models yield the following results: (1) In contrast with bright E’s, bright Sph’s are consistent with solar abundance [Mg/Fe] ratios; (2) Bright Sph’s exhibit metallicities ranging from values typical for metal-rich GGC’s to those for E’s; (3) Although absolute mean ages are quite model dependent, we find evidence that the stellar populations of some (if not all) Sph’s look significantly younger than GGC’s; and (4) Mg2 gradients of bright Sph’s are significantly shallower than those of E galaxies. We conclude that the dichotomy found in the structural properties of Sph and E galaxies is also observed in their stellar populations. A tentative interpretation in terms of differences in s...
We report the discovery and characterization of TOI-1759 b, a temperate (400 K) sub-Neptune-sized... more We report the discovery and characterization of TOI-1759 b, a temperate (400 K) sub-Neptune-sized exoplanet orbiting the M dwarf TOI-1759 (TIC 408636441). TOI-1759 b was observed by TESS to transit in Sectors 16, 17, and 24, with only one transit observed per sector, creating an ambiguity regarding the orbital period of the planet candidate. Ground-based photometric observations, combined with radial-velocity measurements obtained with the CARMENES spectrograph, confirm an actual period of 18.85019 ± 0.00014 days. A joint analysis of all available photometry and radial velocities reveals a radius of 3.17 ± 0.10 R ⊕ and a mass of 10.8 ± 1.5 M ⊕. Combining this with the stellar properties derived for TOI-1759 (R ⋆ = 0.597 ± 0.015 R ⊙; M ⋆ = 0.606 ± 0.020 M ⊙; T eff = 4065 ± 51 K), we compute a transmission spectroscopic metric (TSM) value of over 80 for the planet, making it a good target for transmission spectroscopy studies. TOI-1759 b is among the top five temperate, small exoplane...
We present a new stellar library of 706 stars in the near-infrared spectral region (λλλ8348–9020 ... more We present a new stellar library of 706 stars in the near-infrared spectral region (λλλ8348–9020 A, FWHM = 1.5 A) covering a wide range of atmospheric parameters. The library is developed for the empirical calibration of the Ca II triplet and stellar populations synthesis modeling. We conclude that the Can strength saturates for stellar populations with [Fe/H] > −0.5, showing a mild dependence on metallicity but a very strong sensitivity to the initial mass function.
Calar Alto Academy was initiated in 2007 with the aim to give students from different Spanish uni... more Calar Alto Academy was initiated in 2007 with the aim to give students from different Spanish universities the chance to perform professional observational work at Calar Alto Observatory. The second edition of this innovative educational project has increased the number of participating universities and has almost doubled the quantity of visiting students, in a significant step towards the consolidation of this undergraduate and graduate school of observational astronomy.
We present the results from new spectroscopic observations of a sample of bright spheroidal galax... more We present the results from new spectroscopic observations of a sample of bright spheroidal galaxies (also called dwarf ellipticals) in the Virgo cluster. The central line-strength indices of this sample have been compared with those of bright elliptical galaxies and the predictions of stellar population models. We present evidences for significant differences in the the stellar populations of these two kind of galaxies. In particular, the relative positions of the two galaxy families in the index-index diagrams suggests a steeper initial mass function slope for the star formation in spheroidal galaxies.
An empirical calibration for the λ4000Å break (D 4000) has been obtained using new spectroscopic ... more An empirical calibration for the λ4000Å break (D 4000) has been obtained using new spectroscopic observations of the complete Lick/IDS stellar library (Gorgas et al.: 1999, A&A 139, 29). The results from this calibration have been incorporated into the evolutionary stellar population synthesis models of Bruzual and Charlot (2000, in press), providing reliable predictions of the break behaviour with the age and metallicity of stellar systems. The use of index-index diagrams which include the D 4000 reveals that, for spectra at fixed signal-to-noise ratio, the uncertainties in age and metallicity derived from such diagrams are similar to those obtained using other age indicators, like Hβ or Hγ. We present preliminary results for a sample of 36 field elliptical galaxies observed at the WHT (La Palma). Interestingly, the apparent age spread among elliptical galaxies, previously noted by González (1993, PhD) in the Hβ-<Fe> diagram, is also evident when using the 4000Å break as a completely independent age indicator. Furthermore, it is noted that, using several independent diagrams, like Hβ-<Fe> or D 4000-Fe5015, the ellipticals seem to follow a trend in the sense that metallicity increases as the mean age decreases, in agreement with Trager (1997, PhD), Pedraz et al. (1999, Ap&SS 263, 159), and Trager et al. (2000, astro-ph/0004095). We also show that mean ages derived from the D 4000 diagrams are systematically different from those obtained from the Balmer indices. This is difficult to understand if all the elliptical were formed in a single-burst, but it could be explained if the galaxies were composite systems consisting of an underlying old population plus a later star formation burst. In this case, the apparent mean age would depend on the relative light contributions of the two components to the corresponding spectral range. In particular, simple twoburst models in which a burst of 10% in mass is overimposed on a 17 Gyr old stellar population of significantly lower metallicity can reproduce the observed trends in all the diagrams. Although tentative, this work shows that the simultaneous study of different age indicators can be extremely useful to understand the star formation history of elliptical galaxies.
We present new observational results on the kinematical, morphological, and stellar population pr... more We present new observational results on the kinematical, morphological, and stellar population properties of a sample of 21 dEs located both in the Virgo cluster and in the field, which show that 52% of the dEs i) are rotationally supported, ii) exhibit structural signs of typical rotating systems such as discs, bars or spiral arms, iii) are younger (∼ 3 Gyr) than non-rotating dEs, and iv) are preferentially located either in the outskirts of Virgo or in the field. This evidence is consistent with the idea that rotationally supported dwarfs are late type spirals or irregulars that recently entered the cluster and lost their gas through a ram pressure stripping event, quenching their star formation and becoming dEs through passive evolution. We also find that all, but one, galaxies without photometric hints for hosting discs are pressure supported and are all situated in the inner regions of the cluster. This suggests a different evolution from the rotationally supported systems. Three different scenarios for these non-rotating galaxies are discussed (in situ formation, harassment and ram pressure stripping).
Observations were carried out on 2005 June 30 and July 6 at the 3.5-m telescope at Calar Alto Obs... more Observations were carried out on 2005 June 30 and July 6 at the 3.5-m telescope at Calar Alto Observatory with the Potsdam MultiAperture Spectrograph, PMAS, in the PPAK mode. We obtained publicly available HST/ACS images of the cluster in the F475W, F555W, F625W, F775W and F850LP bands from the HST archive.
We present new measurements of central line-strength indices (namely Mg2, 〈Fe〉, and Hβ) and gradi... more We present new measurements of central line-strength indices (namely Mg2, 〈Fe〉, and Hβ) and gradients for a sample of 6 bright spheroidal galaxies (Sph’s) in the Virgo cluster. Comparison with similar measurements for elliptical galaxies (E’s), galactic globular clusters (GGC’s), and stellar population models yield the following results: (1) In contrast with bright E’s, bright Sph’s are consistent with solar abundance [Mg/Fe] ratios; (2) Bright Sph’s exhibit metallicities ranging from values typical for metal-rich GGC’s to those for E’s; (3) Although absolute mean ages are quite model dependent, we find evidence that the stellar populations of some (if not all) Sph’s look significantly younger than GGC’s; and (4) Mg2 gradients of bright Sph’s are significantly shallower than those of E galaxies. We conclude that the dichotomy found in the structural properties of Sph and E galaxies is also observed in their stellar populations. A tentative interpretation in terms of differences in s...
We report the discovery and characterization of TOI-1759 b, a temperate (400 K) sub-Neptune-sized... more We report the discovery and characterization of TOI-1759 b, a temperate (400 K) sub-Neptune-sized exoplanet orbiting the M dwarf TOI-1759 (TIC 408636441). TOI-1759 b was observed by TESS to transit in Sectors 16, 17, and 24, with only one transit observed per sector, creating an ambiguity regarding the orbital period of the planet candidate. Ground-based photometric observations, combined with radial-velocity measurements obtained with the CARMENES spectrograph, confirm an actual period of 18.85019 ± 0.00014 days. A joint analysis of all available photometry and radial velocities reveals a radius of 3.17 ± 0.10 R ⊕ and a mass of 10.8 ± 1.5 M ⊕. Combining this with the stellar properties derived for TOI-1759 (R ⋆ = 0.597 ± 0.015 R ⊙; M ⋆ = 0.606 ± 0.020 M ⊙; T eff = 4065 ± 51 K), we compute a transmission spectroscopic metric (TSM) value of over 80 for the planet, making it a good target for transmission spectroscopy studies. TOI-1759 b is among the top five temperate, small exoplane...
We present a new stellar library of 706 stars in the near-infrared spectral region (λλλ8348–9020 ... more We present a new stellar library of 706 stars in the near-infrared spectral region (λλλ8348–9020 A, FWHM = 1.5 A) covering a wide range of atmospheric parameters. The library is developed for the empirical calibration of the Ca II triplet and stellar populations synthesis modeling. We conclude that the Can strength saturates for stellar populations with [Fe/H] > −0.5, showing a mild dependence on metallicity but a very strong sensitivity to the initial mass function.
Calar Alto Academy was initiated in 2007 with the aim to give students from different Spanish uni... more Calar Alto Academy was initiated in 2007 with the aim to give students from different Spanish universities the chance to perform professional observational work at Calar Alto Observatory. The second edition of this innovative educational project has increased the number of participating universities and has almost doubled the quantity of visiting students, in a significant step towards the consolidation of this undergraduate and graduate school of observational astronomy.
We present the results from new spectroscopic observations of a sample of bright spheroidal galax... more We present the results from new spectroscopic observations of a sample of bright spheroidal galaxies (also called dwarf ellipticals) in the Virgo cluster. The central line-strength indices of this sample have been compared with those of bright elliptical galaxies and the predictions of stellar population models. We present evidences for significant differences in the the stellar populations of these two kind of galaxies. In particular, the relative positions of the two galaxy families in the index-index diagrams suggests a steeper initial mass function slope for the star formation in spheroidal galaxies.
An empirical calibration for the λ4000Å break (D 4000) has been obtained using new spectroscopic ... more An empirical calibration for the λ4000Å break (D 4000) has been obtained using new spectroscopic observations of the complete Lick/IDS stellar library (Gorgas et al.: 1999, A&A 139, 29). The results from this calibration have been incorporated into the evolutionary stellar population synthesis models of Bruzual and Charlot (2000, in press), providing reliable predictions of the break behaviour with the age and metallicity of stellar systems. The use of index-index diagrams which include the D 4000 reveals that, for spectra at fixed signal-to-noise ratio, the uncertainties in age and metallicity derived from such diagrams are similar to those obtained using other age indicators, like Hβ or Hγ. We present preliminary results for a sample of 36 field elliptical galaxies observed at the WHT (La Palma). Interestingly, the apparent age spread among elliptical galaxies, previously noted by González (1993, PhD) in the Hβ-<Fe> diagram, is also evident when using the 4000Å break as a completely independent age indicator. Furthermore, it is noted that, using several independent diagrams, like Hβ-<Fe> or D 4000-Fe5015, the ellipticals seem to follow a trend in the sense that metallicity increases as the mean age decreases, in agreement with Trager (1997, PhD), Pedraz et al. (1999, Ap&SS 263, 159), and Trager et al. (2000, astro-ph/0004095). We also show that mean ages derived from the D 4000 diagrams are systematically different from those obtained from the Balmer indices. This is difficult to understand if all the elliptical were formed in a single-burst, but it could be explained if the galaxies were composite systems consisting of an underlying old population plus a later star formation burst. In this case, the apparent mean age would depend on the relative light contributions of the two components to the corresponding spectral range. In particular, simple twoburst models in which a burst of 10% in mass is overimposed on a 17 Gyr old stellar population of significantly lower metallicity can reproduce the observed trends in all the diagrams. Although tentative, this work shows that the simultaneous study of different age indicators can be extremely useful to understand the star formation history of elliptical galaxies.
We present new observational results on the kinematical, morphological, and stellar population pr... more We present new observational results on the kinematical, morphological, and stellar population properties of a sample of 21 dEs located both in the Virgo cluster and in the field, which show that 52% of the dEs i) are rotationally supported, ii) exhibit structural signs of typical rotating systems such as discs, bars or spiral arms, iii) are younger (∼ 3 Gyr) than non-rotating dEs, and iv) are preferentially located either in the outskirts of Virgo or in the field. This evidence is consistent with the idea that rotationally supported dwarfs are late type spirals or irregulars that recently entered the cluster and lost their gas through a ram pressure stripping event, quenching their star formation and becoming dEs through passive evolution. We also find that all, but one, galaxies without photometric hints for hosting discs are pressure supported and are all situated in the inner regions of the cluster. This suggests a different evolution from the rotationally supported systems. Three different scenarios for these non-rotating galaxies are discussed (in situ formation, harassment and ram pressure stripping).
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