125 research outputs found
Iron and s-elements abundance variations in NGC5286: comparison with anomalous globular clusters and Milky Way satellites
We present a high resolution spectroscopic analysis of 62 red giants in the
Milky Way globular cluster NGC5286. We have determined abundances of
representative light proton-capture, alpha, Fe-peak and neutron-capture element
groups, and combined them with photometry of multiple sequences observed along
the colour-magnitude diagram. Our principal results are: (i) a broad, bimodal
distribution in s-process element abundance ratios, with two main groups, the
s-poor and s-rich groups; (ii) substantial star-to-star Fe variations, with the
s-rich stars having higher Fe, e.g. _s-rich - _s-poor ~
0.2~dex; and (iii) the presence of O-Na-Al (anti-)correlations in both stellar
groups. We have defined a new photometric index, c_{BVI}=(B-V)-(V-I), to
maximise the separation in the colour-magnitude diagram between the two stellar
groups with different Fe and s-element content, and this index is not
significantly affected by variations in light elements (such as the O-Na
anticorrelation). The variations in the overall metallicity present in NGC5286
add this object to the class of "anomalous" GCs. Furthermore, the chemical
abundance pattern of NGC5286 resembles that observed in some of the anomalous
GCs, e.g. M22, NGC1851, M2, and the more extreme Omega Centauri, that also show
internal variations in s-elements, and in light elements within stars with
different Fe and s-elements content. In view of the common variations in
s-elements, we propose the term s-Fe-anomalous GCs to describe this sub-class
of objects. The similarities in chemical abundance ratios between these objects
strongly suggest similar formation and evolution histories, possibly associated
with an origin in tidally disrupted dwarf satellites.Comment: 28 pages, 21 figures, accepted for publication in MNRA
Augmented Reality in Astrophysics
Augmented Reality consists of merging live images with virtual layers of
information. The rapid growth in the popularity of smartphones and tablets over
recent years has provided a large base of potential users of Augmented Reality
technology, and virtual layers of information can now be attached to a wide
variety of physical objects. In this article, we explore the potential of
Augmented Reality for astrophysical research with two distinct experiments: (1)
Augmented Posters and (2) Augmented Articles. We demonstrate that the emerging
technology of Augmented Reality can already be used and implemented without
expert knowledge using currently available apps. Our experiments highlight the
potential of Augmented Reality to improve the communication of scientific
results in the field of astrophysics. We also present feedback gathered from
the Australian astrophysics community that reveals evidence of some interest in
this technology by astronomers who experimented with Augmented Posters. In
addition, we discuss possible future trends for Augmented Reality applications
in astrophysics, and explore the current limitations associated with the
technology. This Augmented Article, the first of its kind, is designed to allow
the reader to directly experiment with this technology.Comment: 15 pages, 11 figures. Accepted for publication in Ap&SS. The final
publication will be available at link.springer.co
Self-consistent 3D radiative transfer for kilonovae: directional spectra from merger simulations
We present three-dimensional radiative transfer calculations for the ejecta
from a neutron star merger that include line-by-line opacities for tens of
millions of bound-bound transitions, composition from an r-process nuclear
network, and time-dependent thermalization of decay products from individual
and decay reactions. In contrast to expansion opacities and
other wavelength-binned treatments, a line-by-line treatment enables us include
fluorescence effects and associate spectral features with the emitting and
absorbing lines of individual elements. We find variations in the synthetic
observables with both the polar and azimuthal viewing angles. The spectra
exhibit blended features with strong interactions by Ce III, Sr II, Y II, and
Zr II that vary with time and viewing direction. We demonstrate the importance
of wavelength-calibration of atomic data using a model with calibrated Sr, Y,
and Zr data, and find major differences in the resulting spectra, including a
better agreement with AT2017gfo. The synthetic spectra for near-polar
inclination show a feature at around 8000 A, similar to AT2017gfo. However,
they evolve on a more rapid timescale, likely due to the low ejecta mass (0.005
M) as we take into account only the early ejecta. The comparatively
featureless spectra for equatorial observers gives a tentative prediction that
future observations of edge-on kilonovae will appear substantially different
from AT2017gfo. We also show that 1D models obtained by spherically averaging
the 3D ejecta lead to dramatically different direction-integrated luminosities
and spectra compared to full 3D calculations.Comment: 12 pages, 5 figures. Accepted by ApJ
Opacities of Singly and Doubly Ionised Neodymium and Uranium for Kilonova Emission Modeling
Even though the electromagnetic counterpart AT2017gfo to the binary neutron
star merger GW170817 is powered by the radioactive decay of r-process nuclei,
only few tentative identifications of light r-process elements have been made
so far. One of the major limitations for the identification of heavy nuclei is
incomplete or missing atomic data. While substantial progress has been made on
lanthanide atomic data over the last few years, for actinides there has been
less emphasis, with the first complete set of opacity data only recently
published. We perform atomic structure calculations of neodymium as
well as the corresponding actinide uranium . Using two different codes
(FAC and HFR) for the calculation of the atomic data, we investigate the
accuracy of the calculated data (energy levels and electric dipole transitions)
and their effect on kilonova opacities. For the FAC calculations, we optimise
the local central potential and the number of included configurations and use a
dedicated calibration technique to improve the agreement between theoretical
and available experimental atomic energy levels (AELs). For ions with vast
amounts of experimental data available, the presented opacities agree quite
well with previous estimations. On the other hand, the optimisation and
calibration method cannot be used for ions with only few available AELs. For
these cases, where no experimental nor benchmarked calculations are available,
a large spread in the opacities estimated from the atomic data obtained with
the various atomic structure codes is observed.We find that the opacity of
uranium is almost double the neodymium opacity.Comment: 20 pages, 13 figures. Accepted by MNRA
The luminous type Ia supernova 2022ilv and its early excess emission
We present observations and analysis of the host-less and luminous type Ia
supernova 2022ilv, illustrating it is part of the 2003fg-like family, often
referred to as super-Chandrasekhar (Ia-SC) explosions. The ATLAS light curve
shows evidence of a short-lived, pulse-like early excess, similar to that
detected in another luminous type Ia supernova (SN 2020hvf). The light curve is
broad and the early spectra are remarkably similar to SN 2009dc. Adopting a
redshift of for SN 2022ilv based on spectral matching, our
model light curve requires a large Ni mass in the range
M, and a large ejecta mass in the range M. The
early excess can be explained by fast-moving SN ejecta interacting with a thin,
dense shell of circumstellar material close to the progenitor (
cm), a few hours after the explosion. This may be realised in a
double-degenerate scenario, wherein a white dwarf merger is preceded by
ejection of a small amount ( M) of hydrogen and
helium-poor tidally stripped material. A deep pre-explosion Pan-STARRS1 stack
indicates no host galaxy to a limiting magnitude of . This implies
a surprisingly faint limit for any host of , providing further
evidence that these types of explosion occur predominantly in low-metallicity
environments.Comment: Accepted to ApJL after minor revisio
GW190425: Pan-STARRS and ATLAS coverage of the skymap and limits on optical emission associated with FRB190425
GW190425 is the second of only two binary neutron star (BNS) merger events to
be significantly detected by the LIGO-Virgo- Kagra gravitational wave
detectors. With a detection only in LIGO Livingston, the skymap containing the
source was large and no plausible electromagnetic counterpart was found in real
time searching in 2019. Here we summarise our ATLAS and Pan-STARRS wide-field
optical coverage of the skymap beginning within 1 hour and 3 hours respectively
of the GW190425 merger time. More recently, a potential coincidence between
GW190425 and a fast radio burst FRB 190425 has been suggested, given their
spatial and temporal coincidence. The smaller sky localisation area of FRB
190425 and its dispersion measure have led to the identification of a likely
host galaxy, UGC 10667 at a distance of 141 +/- 10 Mpc. Our optical imaging
covered the galaxy 6.0 hrs after GW190425 was detected and 3.5 hrs after the
FRB 190425. No optical emission was detected and further imaging at +1.2 and
+13.2 days also revealed no emission. If the FRB 190425 and GW190425
association were real, we highlight our limits on kilonova emission from a BNS
merger in UGC 10667. The model for producing FRB 190425 from a BNS merger
involves a supramassive magnetised neutron star spinning down by dipole
emission on the timescale of hours. We show that magnetar enhanced kilonova
emission is ruled out by optical upper limits. The lack of detected optical
emission from a kilonova in UGC 10667 disfavours, but does not disprove, the
FRB-GW link for this source.Comment: Submitted to MNRAS, 20th Sept 2023, 9 page
Photometric study of the late-time near-infrared plateau in Type Ia supernovae
We present an in-depth study of the late-time near-infrared plateau in Type
Ia supernovae (SNe Ia), which occurs between 70-500 d. We double the existing
sample of SNe Ia observed during the late-time near-infrared plateau with new
observations taken with the Hubble Space Telescope, Gemini, New Technology
Telescope, the 3.5m Calar Alto Telescope, and the Nordic Optical Telescope. Our
sample consists of 24 nearby SNe Ia at redshift < 0.025. We are able to confirm
that no plateau exists in the Ks band for most normal SNe Ia. SNe Ia with
broader optical light curves at peak tend to have a higher average brightness
on the plateau in J and H, most likely due to a shallower decline in the
preceding 100 d. SNe Ia that are more luminous at peak also show a steeper
decline during the plateau phase in H. We compare our data to state-of-the-art
radiative transfer models of nebular SNe Ia in the near-infrared. We find good
agreement with the sub-Mch model that has reduced non-thermal ionisation rates,
but no physical justification for reducing these rates has yet been proposed.
An analysis of the spectral evolution during the plateau demonstrates that the
ratio of [Fe II] to [Fe III] contribution in a near-infrared filter determines
the light curve evolution in said filter. We find that overluminous SNe decline
slower during the plateau than expected from the trend seen for normal SNe IaComment: 17 pages, 8 figures, Accepted for publication in MNRA
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