TY - Journal
T1 - The rate of period change in pulsating DB white dwarf stars
A1 - Córsico, A. H.
A1 - Althaus, L. G.
JO - Astronomy and Astrophysics
VL - 428
Y1 - 2004/12/1
SP - 159
EP - 170
KW - dense matter/ stars: evolution/ stars: white dwarfs/ stars: oscillations
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...428..159C&db_key=AST&high=42a068d47504913
N2 - In this work, we present the theoretically expected rates of pulsation
period change for V777 Her (DBV) variable stars. To this end we employ
new evolutionary models representative of pulsating DB white dwarf stars
computed in a self-consistent way with the predictions of time-dependent
element diffusion. At the hot edge of the DB instability strip, the
envelopes of the models are characterized by a diffusion-induced
double-layered chemical structure. We compute the numerical values of
rates of period change by solving the equations of linear, adiabatic,
nonradial stellar oscillations. We examine the effects of varying the
stellar mass, the mass of the helium envelope and the neutrino emission
on the expected period changes. We present extensive tabulations of our
results which could be useful for comparison with future detections of
the rate of period change in pulsating DB white dwarfs.
ER -
TY - Journal
T1 - Pulsations of massive ZZ Ceti stars with carbon/oxygen and oxygen/neon cores
A1 - Córsico, A. H.
A1 - García-Berro, E.
A1 - Althaus, L. G.
A1 - Isern, J.
JO - Astronomy and Astrophysics
VL - 427
Y1 - 2004/12/1
SP - 923
EP - 932
KW - stars: evolution/ stars: white dwarfs/ stars: oscillations
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004A%26A...427..923C&db_key=AST&high=42a068d47504913
N2 - We explore the adiabatic pulsational properties of massive white dwarf
stars with hydrogen-rich envelopes and oxygen/neon and carbon/oxygen
cores. To this end, we compute the cooling of massive white dwarf models
for both core compositions taking into account the evolutionary history
of the progenitor stars and the chemical evolution caused by
time-dependent element diffusion. In particular, for the oxygen/neon
models we adopt the chemical profile resulting from repeated
carbon-burning shell flashes expected in very massive white dwarf
progenitors. For carbon/oxygen white dwarfs we consider the chemical
profiles resulting from phase separation upon crystallization. For both
compositions we also take into account the effects of crystallization on
the oscillation eigenmodes. We find that the pulsational properties of
oxygen/neon white dwarfs are noticeably different from those made of
carbon/oxygen, thus making asteroseismological techniques a promising
way to distinguish between the two types of stars and, hence, to obtain
valuable information about their progenitors.
ER -
TY - Journal
T1 - The effects of element diffusion on the pulsational properties of variable DA white dwarf stars
A1 - Córsico, A. H.
A1 - Benvenuto, O. G.
A1 - Althaus, L. G.
A1 - Serenelli, A. M.
JO - Monthly Notices of the Royal Astronomical Society
VL - 332
Y1 - 2002/5/1
SP - 392
EP - 398
KW - stars: evolution/ stars: interiors/ stars: oscillations/ white dwarfs
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.332..392C&db_key=AST&high=42a068d47504913
N2 - We explore the effects of element diffusion due to gravitational
settling and thermal and chemical diffusion on the pulsational
properties of DA white dwarfs. To this end, we employ an updated
evolutionary code coupled with a pulsational, finite difference code for
computing the linear, non-radial g-modes in the adiabatic approximation.
We follow the evolution of a 0.55-Msolar white dwarf model in
a self-consistent way with the evolution of chemical abundance
distribution as given by time-dependent diffusion processes. Results are
compared with the standard treatment of diffusive equilibrium in the
trace element approximation. Appreciable differences are found between
the two employed treatments. We conclude that time-dependent element
diffusion plays an important role in determining the whole oscillation
pattern and the temporal derivative of the periods in DAV white dwarfs.
In addition, we discuss the plausibility of the standard description
employed in accounting for diffusion in most white dwarf
asteroseismological studies.
ER -
TY - Journal
T1 - The mode trapping properties of full DA white dwarf evolutionary models
A1 - Córsico, A. H.
A1 - Althaus, L. G.
A1 - Benvenuto, O. G.
A1 - Serenelli, A. M.
JO - Astronomy and Astrophysics
VL - 387
Y1 - 2002/5/1
SP - 531
EP - 549
KW - stars: evolution/ stars: interiors/ stars: white dwarfs/ stars: oscillations
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...387..531C&db_key=AST&high=42a068d47504913
N2 - An adiabatic, non-radial pulsation study of a 0.563 Msun DA
white dwarf model is presented on the basis of new evolutionary
calculations performed in a self-consistent way with the predictions of
time dependent element diffusion, nuclear burning and the history of the
white dwarf progenitor. Emphasis is placed on the role played by the
internal chemical stratification of these new models in the behaviour of
the eigenmodes, and the expectations for the full g-spectrum of periods.
The implications for the mode trapping properties are discussed at
length. In this regard, we find that, for high periods, the viability of
mode trapping as a mode selection mechanism is markedly weaker for our
models, as compared with the situation in which the hydrogen-helium
transition region is treated assuming equilibrium diffusion in the trace
element approximation.
ER -
TY - Journal
T1 - A New Code for Nonradial Stellar Pulsations and its Application to Low-Mass, Helium White Dwarfs
A1 - Córsico, A. H.
A1 - Benvenuto, O. G.
JO - Astrophysics and Space Science
VL - 279
Y1 - 2002/1/1
SP - 281
EP - 300
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002Ap%26SS.279..281C&db_key=AST&high=42a068d47504913
N2 - We present a finite difference code intended for computing linear,
adiabatic, nonradial pulsations of spherical stars. This code is based
on a slight modification of the general Newton-Raphson technique in
order to handle the relaxation of the eigenvalue (square of the
eigenfrequency) of the modes and their corresponding eigenfunctions.
This code has been tested computing the pulsation spectra of polytropic
spheres finding a good agreement with previous work. Then, we have
coupled this code to our evolutionary code and applied it to the
computation of the pulsation spectrum of a low mass, pure-helium white
dwarf of 0.3 M_solar for a wide range of effective temperatures. In
making this calculation we have taken an evolutionary time step short
enough such that eigenmodes corresponding to a given model are used as
initial approximation to those of the next one. Specifically, we have
computed periods, period spacing, eigenfunctions, weight functions,
kinetic energies and variational periods for a wide range of modes. To
our notice this is the first effort in studying the pulsation properties
of helium white dwarfs. The solution we have found working with these
realistic white dwarf models are in good accord with the predictions of
the asymptotic theory of Tassoul (1980) for high order modes. This
indicates that the code presented here is able to work adequately also
with realistic stellar models.
ER -
TY - Journal
T1 - New DA white dwarf evolutionary models and their pulsational properties
A1 - Córsico, A. H.
A1 - Althaus, L. G.
A1 - Benvenuto, O. G.
A1 - Serenelli, A. M.
JO - Astronomy and Astrophysics
VL - 380
Y1 - 2001/12/1
SP - L17
EP - L20
KW - STARS: EVOLUTION/ STARS: INTERIORS/ STARS: WHITE DWARFS/ STARS: OSCILLATIONS
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001A%26A...380L..17C&db_key=AST&high=42a068d47504913
N2 - In this letter we investigate the pulsational properties of ZZ Ceti
stars on the basis of new white dwarf evolutionary models calculated in
a self-consistent way with the predictions of time dependent element
diffusion and nuclear burning. In addition, full account is taken of the
evolutionary stages prior to the white dwarf formation. Emphasis is
placed on the trapping properties of such models. By means of adiabatic,
non-radial pulsation calculations, we find, as a result of time
dependent diffusion, a much weaker mode trapping effect, particularly
for the high-period regime of the pulsation g-spectrum. This result is
valid at least for models with massive hydrogen-rich envelopes. Thus,
mode trapping would not be an effective mechanism to explain the fact
that all the high periods expected from standard models of stratified
white dwarfs are not observed in the ZZ Ceti stars.
ER -
TY - Journal
T1 - The potential of the variable DA white dwarf G117-B15A as a tool for fundamental physics
A1 - Córsico, A. H.
A1 - Benvenuto, O. G.
A1 - Althaus, L. G.
A1 - Isern, J.
A1 - García-Berro, E.
JO - New Astronomy
VL - 6
Y1 - 2001/6/1
SP - 197
EP - 213
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001NewA....6..197C&db_key=AST&high=42a068d47504913
N2 - White dwarfs are well studied objects. The relative simplicity of their
physics allows one to obtain very detailed models which can be
ultimately compared with their observed properties. Among white dwarfs
there are specific classes of stars, known as ZZ-Ceti objects, which
have a hydrogen-rich envelope and show periodic variations in their
light curves. G117-B15A belongs to this particular set of stars. The
luminosity variations have been successfully explained as due to /g-mode
pulsations. G117-B15A has recently claimed to be the most stable optical
clock ever found, being the rate of change of its 215.2 s period very
small: Ṗ=(2.3+/-1.4)×10-15 ss-1, with a
stability comparable to that of the most stable millisecond pulsars. The
rate of change of the period is closely related to its cooling
timescale, which can be accurately computed. In this paper we study the
pulsational properties of G117-B15A and we use the observed rate of
change of the period to impose constraints on the axion emissivity and
thus, to obtain a preliminary upper bound to the mass of the axion. This
upper bound turns out to be 4 cos2betameV at the 95%
confidence level. Although there are still several observational and
theoretical uncertainties, we conclude that G117-B15A is a very
promising stellar object to set up constraints on particle physics.
ER -
TY - Journal
T1 - Crustal thinning in the Southwestern Iberia Margin
A1 - González, A.
A1 - Torné, M.
A1 - Córdoba, D.
A1 - Vidal, N.
A1 - Matias, L. M.
A1 - Díaz, J.
JO - Geophysical Research Letters
VL - 23
Y1 - 1996/1/1
SP - 2477
EP - 2480
KW - Marine Geology and Geophysics: Marine seismics/ Exploration Geophysics: Seismic methods/ Marine Geology and Geophysics: Gravity/ Exploration Geophysics: Data processing
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996GeoRL..23.2477G&db_key=AST&high=42a068d47524183
N2 - The mode of crustal thinning in the southwestern margin of the Iberian
Peninsula is investigated along a transect that extends from onshore
Iberia to the eastern end of the Horseshoe Abyssal Plain. On onshore
areas, the crustal structure has been deduced using wide-angle seismic
reflection data, whereas offshore we have used coincident steep and
wide-angle reflection data along a NE-SW oriented seismic profile that
extends from Cape San Vicente to the Horseshoe Abyssal Plain. In
addition, 2D gravity modelling has been performed to validate the
crustal structure deduced from seismic data. Our model results reveal
that the crust undergoes a strong but continuous thinning from 31 km
onshore Iberia to less than 15 km in the Horseshoe Abyssal Plain and
that thinning occurs over horizontal distances of about 120 km.
ER -
TY - Journal
T1 - Spectroscopic Binaries and Kinematic Membership in the Open Cluster NGC 3532
A1 - González, Jorge Federico
A1 - Lapasset, Emilio
JO - Astronomical Journal
VL - 123
Y1 - 2002/6/1
SP - 3318
EP - 3324
KW - Stars: Binaries: Spectroscopic/ Galaxy: Open Clusters and Associations: Individual: NGC Number: NGC 3532/ Techniques: Radial Velocities
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AJ....123.3318G&db_key=AST&high=42a068d47527134
N2 - We report spectroscopic observations for bright stars in the open
cluster NGC 3532 up to 1 mag below the turnoff point. We compute radial
velocities by cross-correlations and determine spectral types and
rotational velocities. Using 21 stars identified as certain members, we
derive a mean cluster velocity of +3.4+/-0.3 km s-1. From
radial velocities and angular distances to the cluster center, we
compute membership probabilities for all but two stars that are radial
velocity variables. Only one out of 34 program stars is a clear
kinematic nonmember. Three spectroscopic binaries and three additional
possible radial velocity variables are detected among the 23 stars
measured more than once. We report the star HD 96609 as a double-lined
spectroscopic binary. Using the two-dimensional cross-correlation
technique TODCOR developed by Zucker & Mazeh, we derive the radial
velocity curves for both components and obtain the orbital parameters
with errors of 0.3% and 0.7% for the projected orbital semiaxis and
masses, respectively. This system is composed of two main-sequence stars
in a circular orbit, with a period of 8.19 days. The observations
presented here were obtained at the Complejo Astronómico El
Leoncito (CASLEO), which is operated under agreement between the Consejo
Nacional de Investigaciones Científicas y Técnicas de la
República Argentina (CONICET) and the National Universities of La
Plata, Córdoba, and San Juan.
ER -
TY - Journal
T1 - Radial Velocities and Kinematic Membership in the Open Cluster NGC 3114
A1 - González, Jorge Federico
A1 - Lapasset, Emilio
JO - Astronomical Journal
VL - 121
Y1 - 2001/5/1
SP - 2657
EP - 2663
KW - Stars: Blue Stragglers/ Galaxy: Open Clusters and Associations: Individual: NGC Number: NGC 3114/ Techniques: Radial Velocities
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001AJ....121.2657G&db_key=AST&high=42a068d47527134
N2 - Echelle spectroscopic observations for 30 bright stars in the field of
the sparse open cluster NGC 3114 are presented. The sample includes
main-sequence stars, yellow and red giants, and blue straggler
candidates. Radial velocities are derived by cross-correlations using
high signal-to-noise ratio standard spectra as templates. The cluster
mean velocity is well defined from eight giants and several
main-sequence stars whose average is =-3.52+/-0.25 km
s-1. The membership probabilities of the observed stars are
computed on the basis of the velocity distributions of the cluster and
field stars, and the expected percentage of contamination at each
position. We classified 19 cluster members and 10 nonmembers; the
remaining star is a known spectroscopic binary for which no membership
probability was assigned. Among the members, there is a bright yellow
giant, seven red giants, and four blue straggler candidates, although
they should be considered as turn-off stars. The location of two of them
in the color-magnitude diagram (slightly blueward of the turn-off) can
be explained by their low rotational velocities. No velocity variations
were detected in the 16 stars measured more than once, which indicates
that NGC 3114 possess an abnormally low binary frequency. From spectral
types of cluster members, a distance modulus (V-Mv)=9.8+/-0.2
mag and a reddening E(B-V)=0.07+/-0.01 mag are derived. The cluster age
is estimated to be 1.6×108 yr. The observations
presented here were obtained at the Complejo Astronómico El
Leoncito (CASLEO), which is operated under agreement between the Consejo
Nacional de Investigaciones Científicas y Técnicas de la
República Argentina (CONICET) and the National Universities of La
Plata, Córdoba and San Juan.
ER -
TY - Journal
T1 - Radial Velocities, Binarity, and Kinematic Membership in the Open Cluster NGC 2516
A1 - González, Jorge Federico
A1 - Lapasset, Emilio
JO - Astronomical Journal
VL - 119
Y1 - 2000/5/1
SP - 2296
EP - 2302
KW - STARS: BINARIES: SPECTROSCOPIC/ STARS: BLUE STRAGGLERS/ GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC NUMBER: NGC 2516/ TECHNIQUES: RADIAL VELOCITIES
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000AJ....119.2296G&db_key=AST&high=42a068d47527134
N2 - We present echelle spectroscopic observations for 36 bright (V<9.6)
stars in the open cluster NGC 2516, including several blue straggler
candidates and four red giants. Radial velocities are derived by
cross-correlations using high signal-to-noise ratio standard spectra as
templates. From 22 cluster members a mean cluster velocity of
+22.0+/-0.2 km s-1 was derived. Membership probabilities of
the observed stars are computed on the basis of their distance to the
cluster center and kinematic criteria. We report the discovery of three
double-lined spectroscopic binaries and several probable binaries among
main-sequence stars. A binary frequency of more than 26% is found among
the high-mass main-sequence stars. The blue straggler HD 66341 is a
slowly rotating cluster member with constant velocity, while HD 66194 is
a fast-rotating Be star with probable variations in radial velocity.
Other blue straggler candidates, such as HD 65663, 65950, 66066, and
65987, must be considered turnoff stars. The observations presented here
were obtained at the Complejo Astronómico El Leoncito (CASLEO),
which is operated under agreement between the Consejo Nacional de
Investigaciones Científicas y Técnicas de la
República Argentina (CONICET) and the national universities of La
Plata, Córdoba, and San Juan.
ER -
TY - Journal
T1 - Magnetic twist and writhe of active regions. On the origin of deformed flux tubes
A1 - López Fuentes, M. C.
A1 - Démoulin, P.
A1 - Mandrini, C. H.
A1 - Pevtsov, A. A.
A1 - van Driel-Gesztelyi, L.
JO - Astronomy and Astrophysics
VL - 397
Y1 - 2003/1/1
SP - 305
EP - 318
KW - magnetic fields/ methods: data analysis/ Sun: interior/ Sun: magnetic fields/ Sun: photosphere
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...397..305L&db_key=AST&high=42a068d47519327
N2 - We study the long term evolution of a set of 22 bipolar active regions
(ARs) in which the main photospheric polarities are seen to rotate one
around the other during several solar rotations. We first show that
differential rotation is not at the origin of this large change in the
tilt angle. A possible origin of this distortion is the nonlinear
development of a kink-instability at the base of the convective zone;
this would imply the formation of a non-planar flux tube which, while
emerging across the photosphere, would show a rotation of its
photospheric polarities as observed. A characteristic of the flux tubes
deformed by this mechanism is that their magnetic twist and writhe
should have the same sign. From the observed evolution of the tilt of
the bipoles, we derive the sign of the writhe of the flux tube forming
each AR; while we compute the sign of the twist from transverse field
measurements. Comparing the handedness of the magnetic twist and writhe,
we find that the presence of kink-unstable flux tubes is coherent with
no more than 35% of the 20 cases for which the sign of the twist can be
unambiguously determined. Since at most only a fraction of the tilt
evolution can be explained by this process, we discuss the role that
other mechanisms may play in the inferred deformation. We find that 36%
of the 22 cases may result from the action of the Coriolis force as the
flux tube travels through the convection zone. Furthermore, because
several bipoles overpass in their rotation the mean toroidal (East-West)
direction or rotate away from it, we propose that a possible explanation
for the deformation of all these flux tubes may lie in the interaction
with large-scale vortical motions of the plasma in the convection zone,
including also photospheric or shallow sub-photospheric large scale
flows.
ER -
TY - Journal
T1 - The Counterkink Rotation of a Non-Hale Active Region
A1 - López Fuentes, M. C.
A1 - Demoulin, P.
A1 - Mandrini, C. H.
A1 - van Driel-Gesztelyi, L.
JO - Astrophysical Journal
VL - 544
Y1 - 2000/11/1
SP - 540
EP - 549
KW - Sun: Activity/ Sun: Corona/ Sun: Interior/ Sun: Magnetic Fields
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000ApJ...544..540L&db_key=AST&high=42a068d47519327
N2 - We describe the long-term evolution of a bipolar non-Hale active region
that was observed from 1995 October to 1996 January. During these four
solar rotations the sunspots and subsequent flux concentrations, during
the decay phase of the region, were observed to move in such a way that
by December their orientation conformed to the Hale-Nicholson polarity
law. The sigmoidal shape of the observed soft X-ray coronal loops allows
us to determine the sense of the twist in the magnetic configuration.
This sense is confirmed by extrapolating the observed photospheric
magnetic field, using a linear force-free approach, and comparing the
shape of computed field lines with the observed coronal loops. This
sense of twist agrees with that of the dominant helicity in the solar
hemisphere where the region lies, as well as with the evolution observed
in the longitudinal magnetogram during the first rotation. At first
sight the relative motions of the spots may be misinterpreted as the
rising of an Omega loop deformed by a kink instability, but we deduce
from the sense of their relative displacements a handedness for the
flux-tube axis (writhe) that is opposite to that of the twist in the
coronal loops and, therefore, to what is expected for a kink-unstable
flux tube. After excluding the kink instability, we interpret our
observations in terms of a magnetic flux tube deformed by external
motions while rising through the convective zone. We compare our results
with those of other related studies, and we discuss, in particular,
whether the kink instability is relevant to explain the peculiar
evolution of some active regions.
ER -
TY - Journal
T1 - Astrometry with Virtual Observatories
A1 - López, Carlos E.
JO - Astrophysics and Space Science
VL - 290
Y1 - 2004/4/1
SP - 439
EP - 447
KW - astrometry/ databases/ new techniques
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Ap%26SS.290..439L&db_key=AST&high=42a068d47521753
N2 - With the advent of virtual observatories, most astrometry-oriented
projects being currently developed---and those to come in the near
future---will be greatly enriched. Among these projects it is worth
mentioning double stars and multiple systems, proper-motion detections,
identification of lost high-proper-motion stars, a detailed census of
open cluster members, and precovery of natural satellites, minor planets
and comets. A brief discussion of some of these studies is presented. To
accomplish the goals proposed by the virtual observatories concept, a
massive amount of high-quality astrometric data is needed in advance. It
is shown that today's astrometry is about to ready to face these
new challenges.
ER -
TY - Journal
T1 - Determination of the linear mass power spectrum from the mass function of galaxy clusters
A1 - Sánchez, Ariel G.
A1 - Padilla, Nelson D.
A1 - Lambas, Diego G.
JO - Monthly Notices of the Royal Astronomical Society
VL - 337
Y1 - 2002/11/1
SP - 161
EP - 171
KW - cosmology: theory/ large-scale structure of Universe
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.337..161S&db_key=AST&high=42a068d47513999
N2 - We develop a new method to determine the linear mass power spectrum
using the mass function of galaxy clusters. We obtain the rms mass
fluctuation sigma(M) using the expression for the mass function in the
Press & Schechter, Sheth, Mo & Tormen and Jenkins et al.
formalisms. We apply different techniques to recover the adimensional
power spectrum Delta2(k) from sigma(M) namely the
keff approximation, the singular value decomposition and the
linear regularization method. The application of these techniques to the
tauCDM and LambdaCDM GIF simulations shows a high efficiency in
recovering the theoretical power spectrum over a wide range of scales.
We compare our results with those derived from the power spectrum of the
spatial distribution of the same sample of clusters in the simulations
obtained by application of the classical Feldman, Kaiser & Peacock
(FKP) method. We find that the mass function based method presented here
can provide a very accurate estimate of the linear power spectrum,
particularly for low values of k. This estimate is comparable to, or
even better behaved than, the FKP solution. The principal advantage of
our method is that it allows the determination of the linear mass power
spectrum using the joint information of objects of a wide range of
masses without dealing with specific assumptions on the bias relative to
the underlying mass distribution.
ER -
TY - Journal
T1 - Galaxy groups in the 2dF Galaxy Redshift Survey: luminosity and mass statistics
A1 - Martínez, H. J.
A1 - Zandivarez, A.
A1 - Merchán, M. E.
A1 - Domínguez, M. J. L.
JO - Monthly Notices of the Royal Astronomical Society
VL - 337
Y1 - 2002/12/1
SP - 1441
EP - 1449
KW - galaxies: clusters: general/ galaxies: luminosity function/ mass function/ galaxies: statistics
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.337.1441M&db_key=AST&high=42a068d47529002
N2 - Several statistics are applied to groups and galaxies in groups in the
2° Field Galaxy Redshift Survey. First, we estimate the luminosity
functions for different subsets of galaxies in groups. The results are
well fitted by a Schechter function with parameters M*- 5 log (h)
=-19.90 +/- 0.03 and alpha=-1.13 +/- 0.02 for all galaxies in groups,
which is quite consistent with the results of Norberg et al. for field
galaxies. When considering the four different spectral types defined by
Madgwick et al. we find that the characteristic magnitude is typically
brighter than in the field. We also observe a steeper value,
alpha=-0.76 +/- 0.03, of the faint end slope for low star-forming
galaxies when compared with the corresponding field value. This
steepening is more conspicuous, alpha=-1.10 +/- 0.06, for those
galaxies in more massive groups than that obtained in the lower-mass
subset, . Secondly, we compute group total luminosities using the
prescriptions of Moore, Frenk & White. We define a flux-limited
group sample using a new statistical tool developed by Rauzy. The
resulting group sample is used to determine the group luminosity
function and we find a good agreement with previous determinations and
semi-analytical models. Finally, the group mass function for the
flux-limited sample is derived. An excellent agreement is obtained when
comparing our determination with analytical predictions over two orders
of magnitude in mass.
ER -
TY - Journal
T1 - Galaxy groups in the 2dF Galaxy Redshift Survey: effects of environment on star formation
A1 - Martínez, H. J.
A1 - Zandivarez, A.
A1 - Domínguez, M.
A1 - Merchán, M. E.
A1 - Lambas, D. G.
JO - Monthly Notices of the Royal Astronomical Society
VL - 333
Y1 - 2002/6/1
SP - L31
EP - L34
KW - galaxies: clusters: general/ galaxies: fundamental parameters/ galaxies: general/ galaxies: statistics/ galaxies: stellar content
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.333L..31M&db_key=AST&high=42a068d47529002
N2 - We estimate the fraction of star-forming galaxies in a catalogue of
groups, constructed from the 2dF Galaxy Redshift Survey by
Merchán & Zandivarez. We use the eta spectral type
parameter of galaxies and subdivide the sample of galaxies in groups
into four types depending on the values of the eta parameter following
Madgwick et al. We obtain a strong correlation between the relative
fraction of galaxies with high star formation and the parent group
virial mass. We find that even in the environment of groups with low
virial mass M~1013Msolar the star formation of
their member galaxies is significantly suppressed. The relation between
the fraction of early-type galaxies and the group virial mass obeys a
simple power law spanning over three orders of magnitude in virial mass.
Our results show quantitatively the way that the presence of galaxies
with high star formation rates is inhibited in massive galaxy systems.
ER -
TY - Journal
T1 - Quasar-Galaxy and AGN-Galaxy Cross-Correlations
A1 - Martínez, Héctor J.
A1 - Merchán, Manuel E.
A1 - Valotto, Carlos A.
A1 - Lambas, Diego G.
JO - Astrophysical Journal
VL - 514
Y1 - 1999/4/1
SP - 558
EP - 562
KW - GALAXIES: ACTIVE/ GALAXIES: CLUSTERS: GENERAL/ COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE/ GALAXIES: QUASARS: GENERAL
UR - http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999ApJ...514..558M&db_key=AST&high=42a068d47529002
N2 - We compute quasar-galaxy and AGN-galaxy cross-correlation functions for
samples taken from the Véron-Cetty & Véron catalog of
quasars and active galaxies, using tracer galaxies taken from the
Edinburgh/Durham Southern Catalog. The sample of active galaxy targets
shows positive correlation at projected separations r_p<6 h^-1 Mpc
consistent with the usual power law. On the other hand, we do not find a
statistically significant positive quasar-galaxy correlation signal
except in the range 3 h^-1 Mpclambda_max~1.8%, close to the polarization value
produced by the ISM with normal efficiency (Plambda_max
~ 5 EB-V) with a color excess of EB-V =0.51.
Meanwhile for Hogg 22, located behind NGC 6204, the mean polarization is
Plambda_max~ 2.15%, lower than the expected value for
the observed color excess of EB-V =0.68 (Forbes et al. 1996)
and the average efficiency of polarization for the interstellar dust.
The mean angle of the polarization vectors of Hogg 22 is theta=44.9
°, which agrees with the expected angle produce by dust particles
aligned in the direction of the Galactic Plane
(theta=48°), while for NGC 6204 a lower value,
theta=33.7 °, was found. Therefore, we believe that Hogg 22 is
depolarized by the same dust that is polarizing NGC 6204, due to
different orientations of the dust particles (and magnetic fields) that
polarize the starlight.
Based on observations obtanined at Complejo Astronómico El
Leoncito (CASLEO), operated under agreement between the CONICET and the
National Universities of La Plata, Córdoba, and San Juan,
Argentina.
ER -