1,086 research outputs found
Spectra of globular clusters in the Sombrero galaxy: evidence for spectroscopic metallicity bimodality
We present a large sample of over 200 integrated-light spectra of confirmed
globular clusters (GCs) associated with the Sombrero (M104) galaxy taken with
the DEIMOS instrument on the Keck telescope. A significant fraction of the
spectra have signal-to-noise levels high enough to allow measurements of GC
metallicities using the method of Brodie & Huchra (1990). We find a
distribution of spectroscopic metallicities ranging from -2.2 < [Fe/H] < +0.1
that is bimodal, with peaks at [Fe/H] ~ -1.4 and -0.6. Thus the GC system of
the Sombrero galaxy, like a few other galaxies now studied in detail, reveals a
bimodal spectroscopic metallicity distribution supporting the long-held belief
that colour bimodality reflects two metallicity subpopulations. This further
suggests that the transformation from optical colour to metallicity for old
stellar populations, such as GCs, is not strongly non-linear. We also explore
the radial and magnitude distribution with metallicity for GC subpopulations
but small number statistics prevent any clear trends in these distributions.Comment: 18 pages, 10 figures, 3 tables, MNRAS accepte
Dynamical evidence for a strong tidal interaction between the Milky Way and its satellite, Leo V
We present a chemodynamical analysis of the Leo~V dwarf galaxy, based on Keck
II DEIMOS spectra of 8 member stars. We find a systemic velocity for the system
of kms, and barely resolve a
velocity dispersion for the system, with kms, consistent with previous studies of Leo~V. The
poorly resolved dispersion means we are unable to adequately constrain the dark
matter content of Leo~V. We find an average metallicity for the dwarf of
[Fe/H], and measure a significant spread in the iron abundance
of its member stars, with [Fe/H] dex, which cleanly
identifies Leo~V as a dwarf galaxy that has been able to self-enrich its
stellar population through extended star formation. Owing to the tentative
photometric evidence for tidal substructure around Leo~V, we also investigate
whether there is any evidence for tidal stripping or shocking of the system
within its dynamics. We measure a significant velocity gradient across the
system, of kms per
arcmin (or kms~kpc), which points almost directly
toward the Galactic centre. We argue that Leo~V is likely a dwarf on the brink
of dissolution, having just barely survived a past encounter with the centre of
the Milky Way.Comment: 14 pages, 12 figures, accepted for publication in MNRAS. Updated to
include minor revisions from referee proces
Limits on thermal variations in a dozen quiescent neutron stars over a decade
In quiescent low-mass X-ray binaries (qLMXBs) containing neutron stars, the
origin of the thermal X-ray component may be either release of heat from the
core of the neutron star, or continuing low-level accretion. In general, heat
from the core should be stable on timescales years, while continuing
accretion may produce variations on a range of timescales. While some quiescent
neutron stars (e.g. Cen X-4, Aql X-1) have shown variations in their thermal
components on a range of timescales, several others, particularly those in
globular clusters with no detectable nonthermal hard X-rays (fit with a
powerlaw), have shown no measurable variations. Here, we constrain the spectral
variations of 12 low mass X-ray binaries in 3 globular clusters over
years. We find no evidence of variations in 10 cases, with limits on
temperature variations below 11% for the 7 qLMXBs without powerlaw components,
and limits on variations below 20% for 3 other qLMXBs that do show non-thermal
emission. However, in 2 qLMXBs showing powerlaw components in their spectra
(NGC 6440 CX 1 & Terzan 5 CX 12) we find marginal evidence for a 10% decline in
temperature, suggesting the presence of continuing low-level accretion. This
work adds to the evidence that the thermal X-ray component in quiescent neutron
stars without powerlaw components can be explained by heat deposited in the
core during outbursts. Finally, we also investigate the correlation between
hydrogen column density (N) and optical extinction (A) using our sample
and current models of interstellar X-ray absorption, finding .Comment: 16 pages, 5 figures, MNRAS, in pres
An optical/NIR survey of globular clusters in early-type galaxies III. On the colour bimodality of GC systems
The interpretation that bimodal colour distributions of globular clusters
(GCs) reflect bimodal metallicity distributions has been challenged.
Non-linearities in the colour to metallicity conversions caused by the
horizontal branch (HB) stars may be responsible for transforming a unimodal
metallicity distribution into a bimodal (optical) colour distribution. We study
optical/near-infrared (NIR) colour distributions of the GC systems in 14 E/S0
galaxies. We test whether the bimodal feature, generally present in optical
colour distributions, remains in the optical/NIR ones. The latter colour
combination is a better metallicity proxy than the former. We use KMM and GMM
tests to quantify the probability that different colour distributions are
better described by a bimodal, as opposed to a unimodal distribution. We find
that double-peaked colour distributions are more commonly seen in optical than
in optical/NIR colours. For some of the galaxies where the optical (g-z)
distribution is clearly bimodal, the (g-K) and (z-K) distributions are better
described by a unimodal distribution. The two most cluster-rich galaxies in our
sample, NGC4486 and NGC4649, show some interesting differences. The (g-K)
distribution of NGC4649 is better described by a bimodal distribution, while
this is true for the (g-K) distribution of NGC4486 GCs only if restricted to a
brighter sub-sample with small K-band errors (< 0.05 mag). Formally, the K-band
photometric errors cannot be responsible for blurring bimodal metallicity
distributions to unimodal (g-K) colour distributions. However, simulations
including the extra scatter in the colour-colour diagrams (not fully accounted
for in the photometric errors) show that such scatter may contribute to the
disappearance of bimodality in (g-K) for the full NGC4486 sample. For the less
cluster-rich galaxies results are inconclusive due to poorer statistics.
[Abridged]Comment: A&A accepted, 15 pages, 10 figures, 4 table
The Flare-dominated Accretion Mode of a Radio-bright Candidate Transitional Millisecond Pulsar
© 2020. The American Astronomical Society. All rights reserved.. We report new simultaneous X-ray and radio continuum observations of 3FGL J0427.9-6704, a candidate member of the enigmatic class of transitional millisecond pulsars. These XMM-Newton and Australia Telescope Compact Array observations of this nearly edge-on, eclipsing low-mass X-ray binary were taken in the sub-luminous disk state at an X-ray luminosity of erg s-1. Unlike the few well-studied transitional millisecond pulsars, which spend most of their disk state in a characteristic high or low accretion mode with occasional flares, 3FGL J0427.9-6704 stayed in the flare mode for the entire X-ray observation of ∼20 hr, with the brightest flares reaching ∼2 × 1034 erg s-1. The source continuously exhibited flaring activity on timescales of ∼10-100 s in both the X-ray and optical/ultraviolet (UV). No measurable time delay between the X-ray and optical/UV flares is observed, but the optical/UV flares last longer, and the relative amplitudes of the X-ray and optical/UV flares show a large scatter. The X-ray spectrum can be well-fit with a partially absorbed power law (Γ ∼ 1.4-1.5), perhaps due to the edge-on viewing angle. Modestly variable radio continuum emission is present at all epochs, and is not eclipsed by the secondary, consistent with the presence of a steady radio outflow or jet. The simultaneous radio/X-ray luminosity ratio of 3FGL J0427.9-6704 is higher than any known transitional millisecond pulsars and comparable to that of stellar-mass black holes of the same X-ray luminosity, providing additional evidence that some neutron stars can be as radio-loud as black holes
The mid-UV population of the nucleus and the bulk of the post-merger NGC 3610
The very center of NGC~3610, a clearly disturbed giant elliptical generally
assumed to be a post-merger remnant, appears dominated in the mid-UV (2500-3200
A spectral region) by a stellar population markedly different from that
dominating the bulk of its stellar body. I want here to make use of the mid-UV
spectra of NGC~3610 as seen through tiny (1") and large (10"20")
apertures as a diagnostic population tool. I compare archive IUE/LWP large
aperture and HST/FOS UV data of NGC 3610. The strength of mid-UV triplet
(dominated by the turnoff population) shows a remarkable drop when switching
from the galaxy central arcsec (FOS aperture) to an aperture size comparable to
0.5 r (IUE). The sub-arsec (mid)-UV properties of this galaxy
involved in a past merger reveal a central metal enrichment which left intact
the bulk of its pre-existing population.Comment: 6 pages, 2 figures, accepted for publication in astronomy and
Astrophysic
The Impacat of Personality Type on Blog Participation
The objective of this study is to explore the impact of individual personality type on blog participation. Results indicate that blog participants are more likely to be introverts and perceptives
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