230 research outputs found
Morphologies and stellar populations of galaxies in the core of Abell 2218
SUMMARIZED ABSTRACT:
We present a study of the stellar populations and morphologies of galaxies in
the core of the galaxy cluster Abell 2218. Integral field spectroscopy was
obtained using PMAS/[email protected] CAHA to obtain a complete flux limited sample of
cluster members within its field-of-view (~74"X64"). In addition of 31 galaxies
with known redshifts in the outer regions, we built up a final sample of 59
spectroscopically confirmed cluster members. Multiban photometry and detailed
morphologies were obtained using deep images taken with the HST/ACS camera in
the BVRI and z-bands. The CM diagram shows that the E-type galaxies cover the
range of brighter and redder colors. A large fraction of spiral galaxies
(50%) is found. They cover a wide range in colors. This result, together
with the distributions of ages, metallicities and masses, indicates that E-type
galaxies are more massive and have older stellar populations, while L-type
galaxies are less massive and have a wider range of stellar Our results agree
with a proposed two-step scenario for the evolution of galaxies in clusters. In
addition, an extremely blue merging galaxy system is found at the core, with
the nominal redshift of the cluster.Comment: 29 pages, 17 figures, accepted for publishing in MNRAS. (HST/ACS
composite image: http://www.caha.es/sanchez/abell2218/BRI_big.jpg
CAFE: Calar Alto Fiber-fed Echelle spectrograph
We present here CAFE, the Calar Alto Fiber-fed Echelle spectrograph, a new
instrument built at the Centro Astronomico Hispano Alem\'an (CAHA). CAFE is a
single fiber, high-resolution (70000) spectrograph, covering the
wavelength range between 3650-9800\AA. It was built on the basis of the common
design for Echelle spectrographs. Its main aim is to measure radial velocities
of stellar objects up to 13-14 mag with a precision as good as a few
tens of . To achieve this goal the design was simplified at maximum,
removing all possible movable components, the central wavelength is fixed, so
the wavelentgth coverage; no filter wheel, one slit and so on, with a
particular care taken in the thermal and mechanical stability. The instrument
is fully operational and publically accessible at the 2.2m telescope of the
Calar Alto Observatory.
In this article we describe (i) the design, summarizing its manufacturing
phase; (ii) characterize the main properties of the instrument; (iii) describe
the reduction pipeline; and (iv) show the results from the first light and
commissioning runs. The preliminar results indicate that the instrument fulfill
the specifications and it can achieve the foreseen goals. In particular, they
show that the instrument is more efficient than anticipated, reaching a
20 for a stellar object as faint as 14.5 mag in 2700s
integration time. The instrument is a wonderful machine for exoplanetary
research (by studying large samples of possible systems cotaining massive
planets), galactic dynamics (high precise radial velocities in moving groups or
stellar associations) or astrochemistry.Comment: 12 pages, 23 figures; Acepted for publishing in A&A, 201
Line-Strength Indices in Bright Spheroidals: Evidence for a Stellar Population Dichotomy between Spheroidal and Elliptical Galaxies
We present new measurements of central line-strength indices (namely Mg2,
, and Hbeta 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 star formation histories is suggested.Comment: 14 pages, LaTeX file + 2 PostScript figures, aasms4.sty require
Internal Kinematics of Luminous Compact Blue Galaxies
We describe the dynamical properties which may be inferred from HST/STIS
spectroscopic observations of luminous compact blue galaxies (LCBGs) between
0.1<z<0.7. While the sample is homogeneous in blue rest-frame color, small size
and line-width, and high surface-brightness, their detailed morphology is
eclectic. Here we determine the amplitude of rotation versus random, or
disturbed motions of the ionized gas. This information affirms the accuracy of
dynamical mass and M/L estimates from Keck integrated line-widths, and hence
also the predictions of the photometric fading of these unusual galaxies. The
resolved kinematics indicates this small subset of LCBGs are dynamically hot,
and unlikely to be embedded in disk systems.Comment: To appear in "Starbursts: from 30 Doradus to Lyman Break Galaxies"
2005, eds. R. de Grijs and R. M. Gonzalez Delgado (Kluwer
The CARMENES search for exoplanets around M dwarfs - Photospheric parameters of target stars from high-resolution spectroscopy
The new CARMENES instrument comprises two high-resolution and high-stability
spectrographs that are used to search for habitable planets around M dwarfs in
the visible and near-infrared regime via the Doppler technique. Characterising
our target sample is important for constraining the physical properties of any
planetary systems that are detected. The aim of this paper is to determine the
fundamental stellar parameters of the CARMENES M-dwarf target sample from
high-resolution spectra observed with CARMENES. We also include several M-dwarf
spectra observed with other high-resolution spectrographs, that is CAFE, FEROS,
and HRS, for completeness. We used a {chi}^2 method to derive the stellar
parameters effective temperature T_eff, surface gravity log g, and metallicity
[Fe/H] of the target stars by fitting the most recent version of the
PHOENIX-ACES models to high-resolution spectroscopic data. These stellar
atmosphere models incorporate a new equation of state to describe spectral
features of low-temperature stellar atmospheres. Since T_eff, log g, and [Fe/H]
show degeneracies, the surface gravity is determined independently using
stellar evolutionary models. We derive the stellar parameters for a total of
300 stars. The fits achieve very good agreement between the PHOENIX models and
observed spectra. We estimate that our method provides parameters with
uncertainties of {sigma} T_eff = 51 K, {sigma} log g = 0.07, and {sigma} [Fe/H]
= 0.16, and show that atmosphere models for low-mass stars have significantly
improved in the last years. Our work also provides an independent test of the
new PHOENIX-ACES models, and a comparison for other methods using
low-resolution spectra. In particular, our effective temperatures agree well
with literature values, while metallicities determined with our method exhibit
a larger spread when compared to literature results
Using spectroscopic data to disentangle stellar population properties
It is well known that, when analyzed in the light of current synthesis model predictions, variations in the physical properties of single stellar populations (e.g. age, metallicity, initial mass function, element abundance ratios) may have a similar effect in their integrated spectral energy distributions. The confusion is even worsened when more realistic scenarios, i.e. composite star formation histories, are considered. This is, in fact, one of the major problems when facing the study of stellar populations in star clusters and galaxies. Typically, the observational efforts have aimed to find the most appropriate spectroscopic indicators in order to avoid, as far as possible, degeneracies in the parameter space. However, from a practical point of view, the most suited observables are not, necessarily, those that provide more orthogonality in that parameter space, but those that give the best balance between parameter degeneracy and sensitivity to signal-to-noise ratio per Angstrom, S/N(Angstrom). In order to achieve the minimum combined total error in the derived physical parameters, this work discusses how the functional dependence of typical line-strength indices and colors on S/N(Angstrom) allows to define a suitability parameter which helps to obtain more realistic combinations of spectroscopic data. As an example, we discuss in more detail the problem of breaking the well known age-metallicity degeneracy in relatively old stellar populations, comparing the suitability of different spectroscopic diagrams for a simple stellar population of solar metallicity and of 12 Gyr in age
Magnetic fields in M dwarfs from the CARMENES survey
M dwarfs are known to generate the strongest magnetic fields among
main-sequence stars with convective envelopes, but the link between the
magnetic fields and underlying dynamo mechanisms, rotation, and activity still
lacks a consistent picture. In this work we measure magnetic fields from the
high-resolution near-infrared spectra taken with the CARMENES radial-velocity
planet survey in a sample of 29 active M dwarfs and compare our results against
stellar parameters. We use the state-of-the-art radiative transfer code to
measure total magnetic flux densities from the Zeeman broadening of spectral
lines and filling factors. We detect strong kG magnetic fields in all our
targets. In 16 stars the magnetic fields were measured for the first time. Our
measurements are consistent with the magnetic field saturation in stars with
rotation periods P<4d. The analysis of the magnetic filling factors reveal two
different patterns of either very smooth distribution or a more patchy one,
which can be connected to the dynamo state of the stars and/or stellar mass.
Our measurements extend the list of M dwarfs with strong surface magnetic
fields. They also allow us to better constrain the interplay between the
magnetic energy, stellar rotation, and underlying dynamo action. The high
spectral resolution and observations at near-infrared wavelengths are the
beneficial capabilities of the CARMENES instrument that allow us to address
important questions about the stellar magnetism.Comment: 13 pages of main text, 14 pages of online material, 2 table
Comparative study of ornamental granite cleaning using femtosecond and nanosecond pulsed lasers
Granite has been widely used as a structural and ornamental element in public works and buildings. In damp climates it is almost permanently humid and its exterior surfaces are consequently biologically colonized and blackened We describe a comparative analysis of the performance of two different laser sources in removing biological crusts from granite surfaces: nanosecond Nd:YVO4 laser (355 nm) and femtosecond Ti:Sapphire laser at its fundamental wavelength (790 nm) and second harmonic (395 nm). The granite surface was analyzed using scanning electron microscopy, attenuated total reflection – Fourier transform infrared spectroscopy and profilometry, in order to assess the degree of cleaning and to characterize possible morphological and chemical changes caused by the laser sources.This work is supported by the CTM2010-19584, FIS2009-09522 and CSD2007-00013 research projects (Ministerio de Ciencia y Tecnología, Spanish Government) and by SA086A12-2 project (Junta de Castilla y León, Spain). FTIR, profilometry and SEM analyses were conducted at the University of Vigo's research centre (CACTI)
The human Na<sup>+</sup>/H<sup>+</sup> exchanger 1 is a membrane scaffold protein for extracellular signal-regulated kinase 2
Background
Extracellular signal-regulated kinase 2 (ERK2) is an S/T kinase with more than 200 known substrates, and with critical roles in regulation of cell growth and differentiation and currently no membrane proteins have been linked to ERK2 scaffolding.
Methods and results
Here, we identify the human Na+/H+ exchanger 1 (hNHE1) as a membrane scaffold protein for ERK2 and show direct hNHE1-ERK1/2 interaction in cellular contexts. Using nuclear magnetic resonance (NMR) spectroscopy and immunofluorescence analysis we demonstrate that ERK2 scaffolding by hNHE1 occurs by one of three D-domains and by two non-canonical F-sites located in the disordered intracellular tail of hNHE1, mutation of which reduced cellular hNHE1-ERK1/2 co-localization, as well as reduced cellular ERK1/2 activation. Time-resolved NMR spectroscopy revealed that ERK2 phosphorylated the disordered tail of hNHE1 at six sites in vitro, in a distinct temporal order, with the phosphorylation rates at the individual sites being modulated by the docking sites in a distant dependent manner.
Conclusions
This work characterizes a new type of scaffolding complex, which we term a “shuffle complex”, between the disordered hNHE1-tail and ERK2, and provides a molecular mechanism for the important ERK2 scaffolding function of the membrane protein hNHE1, which regulates the phosphorylation of both hNHE1 and ERK2
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