153 research outputs found
High-speed photometry of the eclipsing polar UZ Fornacis
We present 33 new mid-eclipse times spanning approximately eight years of the
eclipsing polar UZ Fornacis. We have used our new observations to test the
two-planet model previously proposed to explain the variations in its eclipse
times measured over the past 35 years. We find that the proposed model
does indeed follow the general trend of the new eclipse times, however, there
are significant departures. In order to accommodate the new eclipse times, the
two-planet model requires that one or both of the planets require highly
eccentric orbits, that is, 0.4. Such multiple planet orbits are
considered to be unstable. Whilst our new observations are consistent with two
cyclic variations as previously predicted, significant residuals remain. We
conclude that either additional cyclic terms, possibly associated with more
planets, or other mechanisms, such as the Applegate mechanism are contributing
to the eclipse time variations. Further long-term monitoring is required.Comment: 11 pages, 5 figures, Accepted for publication in A&
an overview of the MHONGOOSE survey: Observing nearby galaxies with MeerKAT
© Copyright owned by the author(s). MHONGOOSE is a deep survey of the neutral hydrogen distribution in a representative sample of 30 nearby disk and dwarf galaxies with H I masses from ∼ 106 to ∼ 1011 M, and luminosities from MR ∼ 12 to MR ∼ −22. The sample is selected to uniformly cover the available range in log(MHI). Our extremely deep observations, down to H I column density limits of well below 1018 cm−2 — or a few hundred times fainter than the typical H I disks in galaxies — will directly detect the effects of cold accretion from the intergalactic medium and the links with the cosmic web. These observations will be the first ever to probe the very low-column density neutral gas in galaxies at these high resolutions. Combination with data at other wavelengths, most of it already available, will enable accurate modeling of the properties and evolution of the mass components in these galaxies and link these with the effects of environment, dark matter distribution, and other fundamental properties such as halo mass and angular momentum. MHONGOOSE can already start addressing some of the SKA-1 science goals and will provide a comprehensive inventory of the processes driving the transformation and evolution of galaxies in the nearby universe at high resolution and over 5 orders of magnitude in column density. It will be a Nearby Galaxies Legacy Survey that will be unsurpassed until the advent of the SKA, and can serve as a highly visible, lasting statement of MeerKAT’s capabilities
The hidden HI-massive LIRG HIZOA J0836-43: Inside-out galaxy formation
HIZOA J0836-43 is an extreme gas-rich (=7.5\times10^{10}
M_{\sun}) disk galaxy which lies hidden behind the strongly obscuring Vela
region of the Milky Way. Utilizing observations from the {\it Spitzer Space
Telescope}, we have found it to be a luminous infrared starburst galaxy with a
star formation rate of \sim 21 M_{\sun} \rm{yr^{-1}}, arising from
exceptionally strong molecular PAH emission (L_{7.7\micron} = 1.50 \times
10^{9} L_{\odot}) and far-infrared emission from cold dust. The galaxy
exhibits a weak mid-infrared continuum compared to other starforming galaxies
and U/LIRGs. This relative lack of emission from small grains suggests atypical
interstellar medium conditions compared to other starbursts. We do not detect
significant Ne {\sc v} or O {\sc iv}, which implies an absent or
very weak AGN. The galaxy possesses a prominent bulge of evolved stars and a
stellar mass of 4.4(1.4)\times10^{10} M_{\sun}. With its plentiful gas
supply and current star formation rate, a doubling of stellar mass would occur
on a timescale of 2 Gyr. Compared to local galaxies, HIZOA J0836-43
appears to be a "scaled-up" spiral undergoing inside-out formation, possibly
resembling stellar disk building processes at intermediate redshifts.Comment: 5 pages, 3 figures, 1 table; Accepted for publication in ApJL: August
25 2008. A version with full resolution figures is available at
http://spider.ipac.caltech.edu/staff/jarrett/Cluver_ApJL.pd
SDSS J160043.6+074802.9: a very rapid sdO pulsator
We report the serendipitous discovery of the Sloan Digital Sky Survey star,
SDSS J160043.6+074802.9 to be a very rapid pulsator. The variation is dominated
by a frequency near 8380 microHz (period = 119.33 s) with a large amplitude
(0.04 mag) and its first harmonic at 16760 microHz (59.66 s; 0.005 mag). In
between these frequencies, we find at least another 8 variations with periods
between 62 and 118 seconds and amplitudes between about 0.007 and 0.003 mag;
weaker oscillations might also be present. Preliminary spectrograms from the
performance verification phase of the Southern African Large Telescope indicate
that SDSS J160043.6+074802.9 is a spectroscopic binary consisting of an sdO
star and a late-type main-sequence companion. This makes it the first
unambiguous detection of such an sdO star to pulsate, and certainly the first
found to exhibit multi-frequency variations.Comment: 7 pages, 6 figures (figure 4 at reduced resolution, original
available on request). Accepted for publication in MNRA
Near-infrared studies of the 2010 outburst of the recurrent nova U Scorpii
We present near-infrared (near-IR) observations of the 2010 outburst of U Sco. JHK photometry is presented on 10 consecutive days starting from 0.59 d after outburst. Such photometry can gainfully be integrated into a larger data base of other multiwavelength data which aim to comprehensively study the evolution of U Sco. Early near-IR spectra, starting from 0.56 d after outburst, are presented and their general characteristics discussed. Early in the eruption, we see very broad wings in several spectral lines, with tails extending up to ∼10 000 km s−1 along the line of sight; it is unexpected to have a nova with ejection velocities equal to those usually thought to be exclusive to supernovae. From recombination analysis, we estimate an upper limit of [inline image] for the ejected mass
The RATT PARROT: serendipitous discovery of a peculiarly scintillating pulsar in MeerKAT imaging observations of the Great Saturn-Jupiter Conjunction of 2020. I. Dynamic imaging and data analysis
We report on a radiopolarimetric observation of the Saturn-Jupiter Great
Conjunction of 2020 using the MeerKAT L-band system, initially carried out for
science verification purposes, which yielded a serendipitous discovery of a
pulsar. The radiation belts of Jupiter are very bright and time variable:
coupled with the sensitivity of MeerKAT, this necessitated development of
dynamic imaging techniques, reported on in this work. We present a deep radio
"movie" revealing Jupiter's rotating magnetosphere, a radio detection of
Callisto, and numerous background radio galaxies. We also detect a bright radio
transient in close vicinity to Saturn, lasting approximately 45 minutes.
Follow-up deep imaging observations confirmed this as a faint compact variable
radio source, and yielded detections of pulsed emission by the commensal
MeerTRAP search engine, establishing the object's nature as a radio emitting
neutron star, designated PSR J2009-2026. A further observation combining deep
imaging with the PTUSE pulsar backend measured detailed dynamic spectra for the
object. While qualitatively consistent with scintillation, the magnitude of the
magnification events and the characteristic timescales are odd. We are
tentatively designating this object a pulsar with anomalous refraction
recurring on odd timescales (PARROT). As part of this investigation, we present
a pipeline for detection of variable sources in imaging data, with dynamic
spectra and lightcurves as the products, and compare dynamic spectra obtained
from visibility data with those yielded by PTUSE. We discuss MeerKAT's
capabilities and prospects for detecting more of such transients and variables.Comment: 21 pages, 17 figures, submitted to MNRA
Outbursts of EX Hydrae Revisited
We present optical spectroscopy of EX Hya during its 1991 outburst. This
outburst is characterised by strong irradiation of the front face of the
secondary star by the white dwarf, an overflowing stream which is seen strongly
in HeII and by a dip in the light curves, which extends from 0.1-0.6 in the
binary and spin phases. Strong irradiation of the accretion curtain and that of
the inner regions of the disc led to strong emission of HeII and to the
suppression of the Hg and Hb emission.
Disc overflow was observed in quiescence in earlier studies, where the
overflow stream material was modulated at high velocities close to 1000 km/s.
In outburst, the overflowing material is modulated at even higher velocities
(~1500 km/s). These are streaming velocities down the field lines close to the
white dwarf. Evidence for material collecting near the outer edge of the disc
and corotating with the accretion curtain was observed. In decline, this
material and the accretion curtain obscured almost all the emission near binary
phase 0.4, causing a dip. The dip minimum nearly corresponds with spin pulse
minimum. This has provided additional evidence for an extended accretion
curtain, and for the corotation of material with the accretion curtain at the
outer edge of the disc. From these observations we suggest that a mechanism
similar to that of Spruit & Taam, where outbursts result due to the storage and
release of matter outside the magnetosphere, triggers the outbursts of EX Hya.
This is followed by the irradiation of the secondary star due to accretion
induced radiation.Comment: 12 pages, 14 figures, 1 table. Figures 6, 7, 8 and 11 at low
resolution. Paper accepted by the Monthly Notices of the Royal Astronomical
Societ
Active Disk Building in a local HI-Massive LIRG: The Synergy between Gas, Dust, and Star Formation
HIZOA J0836-43 is the most HI-massive (M_HI = 7.5x10^10 Msun) galaxy detected
in the HIPASS volume and lies optically hidden behind the Milky Way. Markedly
different from other extreme HI disks in the local universe, it is a luminous
infrared galaxy (LIRG) with an actively star forming disk (>50 kpc), central to
its ~ 130 kpc gas disk, with a total star formation rate (SFR) of ~20.5 Msun
yr^{-1}. Spitzer spectroscopy reveals an unusual combination of powerful
polycyclic aromatic hydrocarbon (PAH) emission coupled to a relatively weak
warm dust continuum, suggesting photodissociation region (PDR)-dominated
emission. Compared to a typical LIRG with similar total infrared luminosity
(L_TIR=10^11 Lsun), the PAHs in HIZOA J0836-43 are more than twice as strong,
whereas the warm dust continuum (lambda > 20micron) is best fit by a star
forming galaxy with L_TIR=10^10 Lsun. Mopra CO observations suggest an extended
molecular gas component (H_2 + He > 3.7x10^9 Msun) and a lower limit of ~ 64%
for the gas mass fraction; this is above average compared to local disk
systems, but similar to that of z~1.5 BzK galaxies (~57%). However, the star
formation efficiency (SFE = L_IR/L'_CO) for HIZOA J0836-43 of 140 Lsun (K km
s^{-1} pc^2)^{-1} is similar to that of local spirals and other disk galaxies
at high redshift, in strong contrast to the increased SFE seen in merging and
strongly interacting systems. HIZOA J0836-43 is actively forming stars and
building a massive stellar disk. Its evolutionary phase of star formation
(M_stellar, SFR, gas fraction) compared to more distant systems suggests that
it would be considered typical at redshift z~1. This galaxy provides a rare
opportunity in the nearby universe for studying (at z~0.036) how disks were
building and galaxies evolving at z~1, when similarly large gas fractions were
likely more common.Comment: Accepted for publication in The Astrophysical Journal. 16 pages, 8
figure
- …