Age Dating Stellar Populations in the Near Infrared: An absolute age indicator from the presence/absence of red supergiants

The determination of age is a critical component in the study of a population of stellar clusters. In this letter we present a new absolute age indicator for young massive star clusters based on J-H colour. This novel method identifies clusters as older or younger than 5.7 +/- 0.8 Myr based on the appearance of the first population of red supergiant stars. We test the technique on the stellar cluster population of the nearby spiral galaxy, M83, finding good agreement with the theoretical predictions. The localisation of this technique to the near-IR promises that it may be used well into the future with space-- and ground--based missions optimised for near-IR observations.Comment: 5 pages, 5 figures. Accepted to MNRAS, November 201

The effect of spatial resolution on optical and near-IR studies of stellar clusters: Implications for the origin of the red excess

Recent ground based near-IR studies of stellar clusters in nearby galaxies have suggested that young clusters remain embedded for 7-10Myr in their progenitor molecular cloud, in conflict with optical based studies which find that clusters are exposed after 1-3Myr. Here, we investigate the role that spatial resolution plays in this apparent conflict. We use a recent catalogue of young ($5000$~\msun) clusters in the nearby spiral galaxy, M83, along with Hubble Space Telescope (HST) imaging in the optical and near-IR, and ground based near-IR imaging, to see how the colours (and hence estimated properties such as age and extinction) are affected by the aperture size employed, in order to simulate studies of differing resolution. We find that the near-IR is heavily affected by the resolution, and when aperture sizes $>40$~pc are used, all young/blue clusters move red-ward in colour space, which results in their appearance as heavily extincted clusters. However, this is due to contamination from nearby sources and nebular emission, and is not an extinction effect. Optical colours are much less affected by resolution. Due to the larger affect of contamination in the near-IR, we find that, in some cases, clusters will appear to show near-IR excess when large ($>20$~pc) apertures are used. Our results explain why few young ($<6$~Myr), low extinction (\av < 1~mag) clusters have been found in recent ground based near-IR studies of cluster populations, while many such clusters have been found in higher resolution HST based studies. Additionally, resolution effects appear to (at least partially) explain the origin of the near-IR excess that has been found in a number of extragalactic YMCs.Comment: 8 pages, 5 figures, accepted for publication in MNRA

The Snapshot Hubble U-Band Cluster Survey (SHUCS) II. Star Cluster Population of NGC 2997

We study the star cluster population of NGC 2997, a giant spiral galaxy located at 9.5 Mpc and targeted by the Snapshot Hubble U-band Cluster Survey (SHUCS). Combining our U-band imaging from SHUCS with archival BVI imaging from HST, we select a high confidence sample of clusters in the circumnuclear ring and disk through a combination of automatic detection procedures and visual inspection. The cluster luminosity functions in all four filters can be approximated by power-laws with indices of $-1.7$ to $-2.3$. Some deviations from pure power-law shape are observed, hinting at the presence of a high-mass truncation in the cluster mass function. However, upon inspection of the cluster mass function, we find it is consistent with a pure power-law of index $-2.2\pm0.2$ despite a slight bend at $\sim$$2.5\times10^{4}$ M$_{\odot}$. No statistically significant truncation is observed. From the cluster age distributions, we find a low rate of disruption ($\zeta\sim-0.1$) in both the disk and circumnuclear ring. Finally, we estimate the cluster formation efficiency ($\Gamma$) over the last 100 Myr in each region, finding $7\pm2$% for the disk, $12\pm4$% for the circumnuclear ring, and $10\pm3$% for the entire UBVI footprint. This study highlights the need for wide-field UBVI coverage of galaxies to study cluster populations in detail, though a small sample of clusters can provide significant insight into the characteristics of the population.Comment: 31 pages, 9 figures, accepted to the A

Twistors, Harmonics and Holomorphic Chern-Simons

We show that the off-shell N=3 action of N=4 super Yang-Mills can be written as a holomorphic Chern-Simons action whose Dolbeault operator is constructed from a complex-real (CR) structure of harmonic space. We also show that the local space-time operators can be written as a Penrose transform on the coset SU(3)/(U(1) \times U(1)). We observe a strong similarity to ambitwistor space constructions.Comment: 34 pages, 3 figures, v2: replaced with published version, v3: Added referenc

Anthocyanins protect the gastrointestinal tract from high fat diet-induced alterations in redox signaling, barrier integrity and dysbiosis.

The gastrointestinal (GI) tract can play a critical role in the development of pathologies associated with overeating, overweight and obesity. We previously observed that supplementation with anthocyanins (AC) (particularly glycosides of cyanidin and delphinidin) mitigated high fat diet (HFD)-induced development of obesity, dyslipidemia, insulin resistance and steatosis in C57BL/6J mice. This paper investigated whether these beneficial effects could be related to AC capacity to sustain intestinal monolayer integrity, prevent endotoxemia, and HFD-associated dysbiosis. The involvement of redox-related mechanisms were further investigated in Caco-2 cell monolayers. Consumption of a HFD for 14 weeks caused intestinal permeabilization and endotoxemia, which were associated with a decreased ileum expression of tight junction (TJ) proteins (occludin, ZO-1 and claudin-1), increased expression of NADPH oxidase (NOX1 and NOX4) and NOS2 and oxidative stress, and activation of redox sensitive signals (NF-κB and ERK1/2) that regulate TJ dynamics. AC supplementation mitigated all these events and increased GLP-2 levels, the intestinal hormone that upregulates TJ protein expression. AC also prevented, in vitro, tumor necrosis factor alpha-induced Caco-2 monolayer permeabilization, NOX1/4 upregulation, oxidative stress, and NF-κB and ERK activation. HFD-induced obesity in mice caused dysbiosis and affected the levels and secretion of MUC2, a mucin that participates in intestinal cell barrier protection and immune response. AC supplementation restored microbiota composition and MUC2 levels and distribution in HFD-fed mice. Thus, AC, particularly delphinidin and cyanidin, can preserve GI physiology in HFD-induced obesity in part through redox-regulated mechanisms. This can in part explain AC capacity to mitigate pathologies, i.e. insulin resistance and steatosis, associated with HFD-associated obesity

The Risk of Toxicities from Trastuzumab, Alone or in Combination, in an Elderly Breast Cancer Population

Abstract Background: Breast cancer in the elderly is associated with high recurrence and death rates, due mostly to undertreatment. Human epidermal growth factor receptor type 2 (HER2) overexpression is infrequent in older patients. Trastuzumab- based chemotherapy is often withheld from elderly patients because of its cardiotoxicity. Patients and Methods: Medical records of consecutive HER2-positive breast cancer patients aged 65 70 years old treated between 2005 and 2010 in the participating centers were retrospectively reviewed. All patients underwent multidimensional geriatric assessment (MGA). Results: Among 59 patients identified, 51 patients were evaluable (median age 76 years). The rate of any adverse event was 20% (10/51). The most relevant cardiac adverse event consisted of symptomatic congestive heart failure (CHF; n = 1, 2%) followed by asymptomatic decreases of left ventricular ejection fraction (LVEF; n = 6, 12%). Other toxicities included moderate hypersensitivity reactions during trastuzumab infusions (n = 3, 6%). Hypertension, obesity, prior anthracyclines exposure and concurrent chemotherapy were associated with a higher incidence of toxic events. Previous radiotherapy, concurrent endocrine therapy and different trastuzumab-based regimens did not seem to influence toxicity. Conclusions: Our data suggest that trastuzumab has a good safety profile in nonfrail women aged 70 years and older. These favorable findings may be related to a limited number of anthracycline pretreatments, patient selection and a close cardiologic monitoring

Properties of the cluster population of NGC 1566 and their implications

We present results of a photometric study into the cluster population of NGC 1566, a nearby grand design spiral galaxy, sampled out to a Galactocentric radius of $\approx 5.5$ kpc. The shape of the mass-limited age distribution shows negligible variation with radial distance from the centre of the galaxy, and demonstrates three separate sections, with a steep beginning, flat middle and steep end. The luminosity function can be approximated by a power law at lower luminosities with evidence of a truncation at higher luminosity. The power law section of the luminosity function of the galaxy is best fitted by an index $\approx -2$, in agreement with other studies, and is found to agree with a model luminosity function, which uses an underlying Schechter mass function. The recovered power law slope of the mass distribution shows a slight steepening as a function of galactocentric distance, but this is within error estimates. It also displays a possible truncation at the high mass end. Additionally, the cluster formation efficiency ($\Gamma$) and the specific U-band luminosity of clusters ($T_L(U)$) are calculated for NGC 1566 and are consistent with values for similar galaxies. A difference in NGC 1566, however, is that the fairly high star formation rate is in contrast with a low $\Sigma_{SFR}$ and $\Gamma$, indicating that $\Gamma$ can only be said to depend strongly on $\Sigma_{SFR}$, not the star formation rate