2,177 research outputs found
Rebirth of Novae as Distance Indicators Due to Efficient Large Telescopes
Nova outbursts are the result of strong thermonuclear runaways on the surface
of a white dwarf accreting Hydrogen-rich material from a small mass companion.
These giant explosions cause the star to increase its brightness by hundreds of
thousands of times then making these objects powerful standard candles useful
to measure the extragalactic distances.We have used the Very Large Telescope,
located in the Chilean Atacama desert, to search for novae in NGC 1316--an
early type galaxy in the Fornax cluster. We discovered 4 novae with 3h of
observing time. The use of 8-10m class telescopes coupled with new detectors,
can dramatically improve the efficiency of nova searches in extragalactic
systems.Comment: 4 pages + 2 plot
Nova Populations
In this article we review the current status of the stellar population
assignment for novae. Observations in the Milky Way and in external galaxies
point out the existence of two nova populations: fast and bright novae, mainly
originated from massive white dwarfs and associated with the `thin disk/spiral
arm' stellar population, and slow and faint novae, originated from lighter
white dwarfs and associated with `thick-disk/bulge' population.Comment: Invited Review (14 pag.). To appear in the Proceedings of the
Conference ``Classical Nova Explosions'', M. Hernanz and J. Jose eds.,
American Inst. of Physics, 200
Measurement of the spin of the M87 black hole from its observed twisted light
We present the first observational evidence that light propagating near a
rotating black hole is twisted in phase and carries orbital angular momentum
(OAM). This physical observable allows a direct measurement of the rotation of
the black hole. We extracted the OAM spectra from the radio intensity data
collected by the Event Horizon Telescope from around the black hole M87* by
using wavefront reconstruction and phase recovery techniques and from the
visibility amplitude and phase maps. This method is robust and complementary to
black-hole shadow circularity analyses. It shows that the M87* rotates
clockwise with an estimated rotation parameter with
confidence level (c.l.) and inclination , equivalent to
a magnetic arrested disk with inclination . From our
analysis we conclude, within a 6 c.l., that the M87* is rotating.Comment: Small addition on coherence. 5 pages, 2 figures Accepted for
publication in MNRAS Letter
Predicted rates of merging neutron stars in galaxies
In this work, we compute rates of merging neutron stars (MNS) in galaxies of
different morphological type, as well as the cosmic MNS rate in a unitary
volume of the Universe adopting different cosmological scenarios. Our aim is to
provide predictions of kilonova rates for future observations both at low and
high redshift. In the adopted galaxy models, we take into account the
production of r-process elements either by MNS or core-collapse supernovae. In
computing the MNS rates we adopt either a constant total time delay for merging
(10 Myr) or a distribution function of such delays. Our main conclusions are:
i) the observed present time MNS rate in our Galaxy is well reproduced either
with a constant time delay or a distribution function . The
[Eu/Fe] vs. [Fe/H] relation in the Milky Way can be well reproduced with only
MNS, if the time delay is short and constant. If the distribution function of
delays is adopted, core-collapse supernovae as are also required. ii) The
present time cosmic MNS rate can be well reproduced in any cosmological
scenario, either pure luminosity evolution or a typical hierarchical one, and
spirals are the main contributors to it. iii) The spirals are the major
contributors to the cosmic MNS at all redshifts in hierarchical scenarios. In
the pure luminosity evolution scenario, the spirals are the major contributors
locally, whereas at high redshift ellipticals dominate. iv) The predicted
cosmic MNS rate well agrees with the cosmic rate of short Gamma Ray Bursts if
the distribution function of delays is adopted, in a cosmological hierarchical
scenario observationally derived. v) Future observations of Kilonovae in
ellipticals will allow to disentangle among constant or a distribution of time
delays as well as among different cosmological scenarios
Globular Cluster Calibration of the Peak Brightness of the Type Ia Supernova 1992A and the Value of Ho
We have determined the absolute magnitude at maximum light of SN 1992A by
using the turn-over magnitude of the Globular Cluster Luminosity Function of
its parent galaxy, NGC 1380. A recalibration of the peak of the turn-over
magnitude of the Milky Way clusters using the latest HIPPARCOS results has been
made with an assessment of the complete random and systematic error budget. The
following results emerge: a distance to NGC 1380 of 18.6 +/- 1.4 Mpc,
corresponding to (m-M)=31.35 +/- 0.16, and an absolute magnitude of SN 1992A at
maximum of M_B(max)= -18.79 +/- 0.16. Taken at face value, SN 1992A seems to be
more than half a magnitude fainter than the other SNeI-a for which accurate
distances exist. We discuss the implications of this result and present
possible explanations. We also discuss the Phillips'(1993) relationship between
rate of decline and the absolute magnitude at maximum, on the basis of 9
SNeI-a, whose individual distances have been obtained with Cepheids and the
Globular Cluster Luminosity Function. The new calibration of this relationship,
applied to the most distant SNe of the Calan-Tololo survey, yields Ho=62 +/- 6
km/s/Mpc.Comment: 12 pages (MNRAS style, two columns, including 6 figures), accepted
for publication in the MNRAS, a full resolution version of Fig.1 is available
at http://www.ucolick.org/~mkissle
New measurements of from gamma-ray bursts
Context: Data from cosmic microwave background radiation (CMB), baryon
acoustic oscillations (BAO), and supernovae Ia (SNe-Ia) support a constant dark
energy equation of state with . Measuring the evolution of
along the redshift is one of the most demanding challenges for observational
cosmology. Aims: We discuss the existence of a close relation for GRBs, named
Combo-relation, based on characteristic parameters of GRB phenomenology such as
the prompt intrinsic peak energy , the X-ray afterglow, the initial
luminosity of the shallow phase , the rest-frame duration of the
shallow phase, and the index of the late power-law decay . We use it
to measure and the evolution of the dark energy equation of state.
We also propose a new calibration method for the same relation, which reduces
the dependence on SNe Ia systematics. Methods: We have selected a sample of
GRBs with 1) a measured redshift ; 2) a determined intrinsic prompt peak
energy , and 3) a good coverage (0.3-10) keV afterglow light curves.
The fitting technique of the rest.frame (0.3-10) keV luminosity light curves
represents the core of the Combo-relation. We separate the early steep decay,
considered a part of the prompt emission, from the X-ray afterglow additional
component. Data with the largest positive residual, identified as flares, are
automatically eliminated until the p-value of the fit becomes greater than 0.3.
Results: We strongly minimize the dependency of the Combo-GRB calibration on
SNe Ia. We also measure a small extra-Poissonian scatter of the Combo-relation,
which allows us to infer from GRBs alone
(1) for the CDM cosmological model, and , for the flat-Universe
variable equation of state case.Comment: 10 pages, 9 figures, 3 tables. Accepted for publication in A&A.
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