14 research outputs found
ESO 603-G21: A strange polar-ring galaxy
We present the results of B, V, R surface photometry of ESO603-G21 - a galaxy
with a possible polar ring. The morphological and photometric features of this
galaxy are discussed. The central round object of the galaxy is rather red and
presents a nearly exponential surface brightness distribution. This central
structure is surrounded by a blue warped ring or disk. The totality of the
observed characteristics (optical and NIR colors, strong color gradients, HI
and H_2 content, FIR luminosity and star-formation rate, rotation-curve shape,
global mass-to-luminosity ratio, the agreement with the Tully-Fisher relation,
etc.) shows that ESO603-G21 is similar to late-type spiral galaxies. We suppose
that morphological peculiarities and the possible existence of two large-scale
kinematically-decoupled subsystems in ESO603-G21 can be explained as being a
result of dissipative merging of two spiral galaxies or as a consequence of a
companion accretion onto a pre-existing spiral host.Comment: 8 pages, Astron. Astrophys, accepte
A first study of the galaxy HRG 2304 and its companion AM 1646-795 (NED01)
Aims. We report the first study of the peculiar ring-like galaxy HRG 2304
(NED02),which was previously classified as a ring galaxy with an elliptical
smooth ring. This object was selected to prove that it is a candidate for the
Solitaire-type ring galaxies in an early stage of ring formation. The main goal
of this work is to provide the spectral characteristics of the current object
and its companion AM 1646-795 (NED01). Methods. The study is based on
spectroscopic observations in the optical band to highlight the characteristics
of this interacting galaxy. To investigate the star formation history of HRG
2304 we used the stellar population synthesis code STARLIGHT. The direct V and
B broad band images were used to enhance some fine structures. Results. Along
the entire long-slit signal, the spectra of HRG 2304 and its companion resemble
that of an early-type galaxy. We estimated a heliocentric systemic redshift of
z = 0.0415, corresponding to heliocentric velocities of 12449 km s-1 for HRG
2304 (NED02) and 12430 km s-1 for AM1646-795 (NED01). The spatial variation in
the contribution of the stellar population components for both objects are
dominated by an old stellar population 2x10^9 < t < 13x10^9 yr. The observed
radial-velocity distribution and the fine structures around HRG 2304 suggest an
ongoing tidal interaction of both galaxies. Conclusions.The spectroscopic
results and the morphological peculiarities of HRG 2304 can be adequately
interpreted as an ongoing interaction with the companion galaxy. Both galaxies
are early-type, the companion is elliptical, and the smooth distribution of the
material around HRG 2304 and its off-center nucleus in the direction of
AM1646-795 (NED01) characterize HRG 2304 as a Solitaire-type galaxy candidate
in an early stage of ring formation.Comment: Accepted for publication in Astronomy and Astrophysics, 9 pages, 10
figures and 3 table
Testing the Newton second law in the regime of small accelerations
It has been pointed out that the Newtonian second law can be tested in the very small acceleration regime by using the combined movement of the Earth and Sun around the Galactic center of mass. It has been shown that there are only two brief intervals during the year in which the experiment can be completed, which correspond to only two specific spots on the Earth surface. An alternative experimental setup is presented to allow the measurement to be made on Earth at any location and at any time.It has been pointed out that the Newtonian second law can be tested in the very small acceleration regime by using the combined movement of the Earth and Sun around the Galactic center of mass. It has been shown that there are only two brief intervals during the year in which the experiment can be completed, which correspond to only two specific spots on the Earth surface. An alternative experimental setup is presented to allow the measurement to be made on Earth at any location and at any time
FM 047-02: a collisional pair of galaxies with a ring
Aims. We investigate the nature of the galaxy pair FM 047-02, which has been
proposed as an archetype of the Solitaire types of peculiar (collisional) ring
galaxies. Methods. The study is based on long-slit spectrophotometric data in
the range of 3500-9500 angstrons obtained with the Gemini Multi-ObjectComment: 07 pages, 06 figures, 02 tables. arXiv admin note: text overlap with
arXiv:1206.071
Data Mining and Machine Learning in Astronomy
We review the current state of data mining and machine learning in astronomy.
'Data Mining' can have a somewhat mixed connotation from the point of view of a
researcher in this field. If used correctly, it can be a powerful approach,
holding the potential to fully exploit the exponentially increasing amount of
available data, promising great scientific advance. However, if misused, it can
be little more than the black-box application of complex computing algorithms
that may give little physical insight, and provide questionable results. Here,
we give an overview of the entire data mining process, from data collection
through to the interpretation of results. We cover common machine learning
algorithms, such as artificial neural networks and support vector machines,
applications from a broad range of astronomy, emphasizing those where data
mining techniques directly resulted in improved science, and important current
and future directions, including probability density functions, parallel
algorithms, petascale computing, and the time domain. We conclude that, so long
as one carefully selects an appropriate algorithm, and is guided by the
astronomical problem at hand, data mining can be very much the powerful tool,
and not the questionable black box.Comment: Published in IJMPD. 61 pages, uses ws-ijmpd.cls. Several extra
figures, some minor additions to the tex
The HST Survey of BL Lacertae Objects: Morphological Properties of Low redshift Host Galaxies
We report on the optical properties of a sample of 30 BL Lac host galaxies in
the redshift range , as derived from HST observations. All galaxies
are fully resolved in the WFPC2 (F702W filter) images, allowing a quantitative
analysis in two dimensions. Most and possibly all these galaxies have
characteristics very similar to those of ``normal'' giant ellipticals. The
luminosity, ellipticity, isophote twisting and amount of disky or boxy
isophotes are consistent with those found in non-active ellipticals and in
radio galaxies. In all cases the BL Lac nucleus is well centered in the main
body of its host galaxy, a result that argues strongly against the microlensing
hypothesis for any significant fraction of the population. A search for faint
sub-structures in the host galaxies has not revealed notable signatures of
tidal distortions or sub-components (faint disks, bars, X features, etc.), and
with only one exception, there are no prominent dusty features in the central
regions. Instead, the BL Lac host galaxies are smooth and unperturbed,
suggesting that strong external gravitational interactions are not important to
ongoing activity. A careful examination of the environment around the nucleus,
however, shows a high incidence of close companion objects, whose nature
remains unclear pending spectroscopic observations.Comment: 16 pages, 8 figures. Ap.J accepte
Are He and N Abundances in Type I PNe as High as Empirically Derived?
Type I planetary nebulae (PNe) are defined as those with high He and N
abundances (Peimbert & Torres-Peimbert 1983). These objects present in general
bipolar geometries and have high stellar temperatures (Corradi & Schwarz 1995,
Torres-Peimbert & Peimbert 1997). In this paper we analyse the empirical
methods for abundance determination in order to check if the He and N
overabundances in Type I PNe are a consequence of a geometrical effect, due to
the bipolarity, or the ionization stratification, due to the stellar
temperature. For this, we obtain simulated spherically symmetrical as well as
bipolar nebulae, using a 3D photoionization code. From the projected emission
line intensities for: a) the whole nebula; b) for a slit crossing the nebula;
as well as c) for different positions in the nebula, we applied the formulae
used in the literature to obtain empirical abundances. These empirical
abundances are then compared with the adopted ones. We show that empirical
abundances depend on the particular line of sight covered by the observation
and can simulate an overabundance and/or the presence of abundance gradients of
He and N in planetary nebulae with high stellar temperature. The geometrical
effects are also discussed. Systematic errors in abundance determinations by
empirical methods are higher for the N/H ratio than for N/O. Thus, it seems
better to use the N/O value when discussing N rich objects.Comment: 19 pages, 5 figures, aastex package, to be published at Ap.
The coronal line regions of planetary nebulae NGC6302 and NGC6537: 3-13um grating and echelle spectroscopy
We report on advances in the study of the cores of NGC6302 and NGC6537 using
infrared grating and echelle spectroscopy. In NGC6302, emission lines from
species spanning a large range of ionization potential, and in particular
[SiIX]3.934um, are interpreted using photoionization models (including CLOUDY),
which allow us to reestimate the central star's temperature to be about
250000K. All of the detected lines are consistent with this value, except for
[AlV] and [AlVI]. Aluminium is found to be depleted to one hundredth of the
solar abundance, which provides further evidence for some dust being mixed with
the highly ionized gas (with photons harder than 154eV). A similar depletion
pattern is observed in NGC6537. Echelle spectroscopy of IR coronal ions in
NGC6302 reveals a stratified structure in ionization potential, which confirms
photoionization to be the dominant ionization mechanism. The lines are narrow
(< 22km/s FWHM), with no evidence of the broad wings found in optical lines
from species with similar ionization potentials, such as [NeV]3426A. We note
the absence of a hot bubble, or a wind blown bipolar cavity filled with a hot
plasma, at least on 1'' and 10km/s scales. We also provide accurate new
wavelengths for several of the infrared coronal lines observed with the
echelle.Comment: Accepted for publication in MNRA