517 research outputs found
Resolved Stellar Populations at the Distance of Virgo
Top of the wish list of any astronomer who wants to understand galaxy
formation and evolution is to resolve the stellar populations of a sample of
giant elliptical galaxies: to take spectra of the stars and make
Colour-Magnitude Diagrams going down to the oldest main sequence turn-offs. It
is only by measuring the relative numbers of stars on Main Sequence Turnoffs at
ages ranging back to the time of the earliest star formation in the Universe
that we can obtain unambiguous star formation histories. Understanding star
formation histories of individual galaxies underpins all our theories of galaxy
formation and evolution. To date we only have detailed star formation histories
for the nearest-by objects in the Local Group, namely galaxies within 700kpc of
our own. This means predominantly small diffuse dwarf galaxies in a poor group
environment. To sample the full range of galaxy types and to consider galaxies
in a high density environment (where much mass in the Universe resides) we need
to be able to resolve stars at the distance of the Virgo (~17Mpc) or Fornax
(~18Mpc) clusters. This ambitious goal requires an Extremely Large Telescope
(ELT), with a diameter of 50-150m, operating in the optical/near-IR at its
diffraction limit.Comment: proceedings IAU 232 "Extremely Large Telescopes", eds Whitelock,
Leibundgut and Dennefel
Selecting AGN through variability in SN datasets
Variability is a main property of active galactic nuclei (AGN) and it was
adopted as a selection criterion using multi epoch surveys conducted for the
detection of supernovae (SNe). We have used two SN datasets. First we selected
the AXAF field of the STRESS project, centered in the Chandra Deep Field South
where, besides the deep X-ray surveys also various optical catalogs exist. Our
method yielded 132 variable AGN candidates. We then extended our method
including the dataset of the ESSENCE project that has been active for 6 years,
producing high quality light curves in the R and I bands. We obtained a sample
of ~4800 variable sources, down to R=22, in the whole 12 deg^2 ESSENCE field.
Among them, a subsample of ~500 high priority AGN candidates was created using
as secondary criterion the shape of the structure function. In a pilot
spectroscopic run we have confirmed the AGN nature for nearly all of our
candidates.Comment: 6 pages, 3 figures, contributed talk, proceedings of the 9th Hellenic
Astronomical Society Conference, Athens, 20-24 September 200
A reddening-free method to estimate the Ni mass of Type Ia supernovae
The increase in the number of Type Ia supernovae (SNe\,Ia) has demonstrated
that the population shows larger diversity than has been assumed in the past.
The reasons (e.g. parent population, explosion mechanism) for this diversity
remain largely unknown. We have investigated a sample of SNe\,Ia near-infrared
light curves and have correlated the phase of the second maximum with the
bolometric peak luminosity. The peak bolometric luminosity is related to the
time of the second maximum (relative to the {\it B} light curve maximum) as
follows : .
Ni masses can be derived from the peak luminosity based on Arnett's
rule, which states that the luminosity at maximum is equal to instantaneous
energy generated by the nickel decay. We check this assumption against recent
radiative-transfer calculations of Chandrasekhar-mass delayed detonation models
and find this assumption is valid to within 10\% in recent radiative-transfer
calculations of Chandrasekhar-mass delayed detonation models.
The vs. relation is applied to a sample of 40 additional
SNe\,Ia with significant reddening ( 0.1 mag) and a reddening-free
bolometric luminosity function of SNe~Ia is established. The method is tested
with the Ni mass measurement from the direct observation of
rays in the heavily absorbed SN 2014J and found to be fully
consistent.
Super-Chandrasekhar-mass explosions, in particular SN\,2007if, do not follow
the relations between peak luminosity and second IR maximum. This may point to
an additional energy source contributing at maximum light.
The luminosity function of SNe\,Ia is constructed and is shown to be
asymmetric with a tail of low-luminosity objects and a rather sharp
high-luminosity cutoff, although it might be influenced by selection effects.Comment: 9 pages, 3 figures, Accepted to A&
Applying the expanding photosphere and standardized candle methods to Type II-Plateau supernovae at cosmologically significant redshifts: the distance to SN 2013eq
Based on optical imaging and spectroscopy of the Type II-Plateau SN 2013eq,
we present a comparative study of commonly used distance determination methods
based on Type II supernovae. The occurrence of SN 2013eq in the Hubble flow (z
= 0.041 +/- 0.001) prompted us to investigate the implications of the
difference between "angular" and "luminosity" distances within the framework of
the expanding photosphere method (EPM) that relies upon a relation between flux
and angular size to yield a distance. Following a re-derivation of the basic
equations of the EPM for SNe at non-negligible redshifts, we conclude that the
EPM results in an angular distance. The observed flux should be converted into
the SN rest frame and the angular size, theta, has to be corrected by a factor
of (1+z)^2. Alternatively, the EPM angular distance can be converted to a
luminosity distance by implementing a modification of the angular size. For SN
2013eq, we find EPM luminosity distances of D_L = 151 +/- 18 Mpc and D_L = 164
+/- 20 Mpc by making use of different sets of dilution factors taken from the
literature. Application of the standardized candle method for Type II-P SNe
results in an independent luminosity distance estimate (D_L = 168 +/- 16 Mpc)
that is consistent with the EPM estimate.Comment: 12 pages, 4 figures, accepted by A&
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