Handedness in fiddler crab fights

Asymmetric weapons are common in bilateral animals and, in some species, they can occur on either the left- or the right-hand side of the body (lateralization). Fiddler crabs (Uca spp, Decapoda: Ocypodidae) have an enlarged claw that is used in male–male combat over territories and in courtship displays. Males can be either right- or left-handed, and most species have a 1:1 ratio. Past studies have found little effect of handedness on fighting success, fight duration or other measures of combat. Here we show that, while handedness per se, does not affect fighting, handedness matching has a significant effect. In Uca mjoebergi, fights between different-handed males were more likely to escalate to grappling, suggesting that it is harder for the combatants to determine the winner. We suggest that the positioning of the claws during fighting creates distinct forces that result in different outcomes for same- versus different-handed fights. This can represent a strong selective pressure in populations with an uneven handedness distribution where the handedness minority will often engage in different-handed fights. We discuss these results in light of the selective forces that may act on handedness distribution in fiddler crabs

Type II supernova spectral diversity, II: spectroscopic and photometric correlations

We present an analysis of observed trends and correlations between a large range of spectral and photometric parameters of more than 100 type II supernovae (SNe II), during the photospheric phase. We define a common epoch for all SNe of 50 days post-explosion, where the majority of the sample is likely to be under similar physical conditions. Several correlation matrices are produced to search for interesting trends between more than 30 distinct light-curve and spectral properties that characterize the diversity of SNe II. Overall, SNe with higher expansion velocities are brighter, have more rapidly declining light curves, shorter plateau durations, and higher 56Ni masses. Using a larger sample than previous studies, we argue that "Pd" - the plateau duration from the transition of the initial to "plateau" decline rates to the end of the "plateau" - is a better indicator of the hydrogen envelope mass than the traditionally used optically thick phase duration (OPTd: explosion epoch to end of plateau). This argument is supported by the fact that Pd also correlates with s 3, the light-curve decline rate at late times: lower Pd values correlate with larger s 3 decline rates. Large s 3 decline rates are likely related to lower envelope masses, which enables gamma-ray escape. We also find a significant anticorrelation between Pd and s 2 (the plateau decline rate), confirming the long standing hypothesis that faster declining SNe II (SNe IIL) are the result of explosions with lower hydrogen envelope masses and therefore have shorter Pd values.Fil: Gutiérrez, Claudia P.. Universidad de Chile; Chile. University of Southampton; Reino Unido. European Southern Observatory Santiago; Chile. Millennium Institute Of Astrophysics; ChileFil: Anderson, Joseph P.. European Southern Observatory Santiago; ChileFil: Hamuy, Mario. Millennium Institute Of Astrophysics; Chile. Universidad de Chile; ChileFil: González Gaitan, Santiago. Universidad de Chile; Chile. Universidade de Lisboa; Portugal. Millennium Institute Of Astrophysics; ChileFil: Galbany, Lluis. University of Pittsburgh at Johnstown; Estados Unidos. University of Pittsburgh; Estados UnidosFil: Dessart, Luc. Universidad de Chile; ChileFil: Stritzinger, Maximilian D.. University Aarhus; DinamarcaFil: Phillips, Mark M.. Las Campanas Observatory; ChileFil: Morrell, Nidia. Las Campanas Observatory; ChileFil: Folatelli, Gaston. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin

A Comprehensive Archival Search for Counterparts to Ultra-Compact High Velocity Clouds: Five Local Volume Dwarf Galaxies

We report five Local Volume dwarf galaxies (two of which are presented here for the first time) uncovered during a comprehensive archival search for optical counterparts to ultra-compact high velocity clouds (UCHVCs). The UCHVC population of HI clouds are thought to be candidate gas-rich, low mass halos at the edge of the Local Group and beyond, but no comprehensive search for stellar counterparts to these systems has been presented. Careful visual inspection of all publicly available optical and ultraviolet imaging at the position of the UCHVCs revealed six blue, diffuse counterparts with a morphology consistent with a faint dwarf galaxy beyond the Local Group. Optical spectroscopy of all six candidate dwarf counterparts show that five have an H$\alpha$-derived velocity consistent with the coincident HI cloud, confirming their association, the sixth diffuse counterpart is likely a background object. The size and luminosity of the UCHVC dwarfs is consistent with other known Local Volume dwarf irregular galaxies. The gas fraction ($M_{HI}/M_{star}$) of the five dwarfs are generally consistent with that of dwarf irregular galaxies in the Local Volume, although ALFALFA-Dw1 (associated with ALFALFA UCHVC HVC274.68+74.70$-$123) has a very high $M_{HI}/M_{star}$$\sim$40. Despite the heterogenous nature of our search, we demonstrate that the current dwarf companions to UCHVCs are at the edge of detectability due to their low surface brightness, and that deeper searches are likely to find more stellar systems. If more sensitive searches do not reveal further stellar counterparts to UCHVCs, then the dearth of such systems around the Local Group may be in conflict with $\Lambda$CDM simulations.Comment: 18 pages, 4 tables, 4 figures, ApJ Accepte

Type II supernovae as probes of environment metallicity: observations of host HII regions

Spectral modelling of SNII atmospheres indicates a clear dependence of metal line strengths on progenitor metallicity. This motivates further work to evaluate the accuracy with which these SNe can be used as metallicity indicators. To assess this accuracy we present a sample of SNII HII-region spectroscopy, from which environment abundances are derived. These environment abundances are compared to the observed strength of metal lines in SN spectra. Combining our sample with measurements from the literature, we present oxygen abundances of 119 host HII regions, by extracting emission line fluxes and using abundance diagnostics. Then, following Dessart et al., these abundances are compared to equivalent widths of Fe 5018 A at various time and colour epochs. Our distribution of inferred SNII host HII-region abundances has a range of ~0.6 dex. We confirm the dearth of SNeII exploding at metallicities lower than those found (on average) in the Large Magellanic Cloud. The equivalent width of Fe 5018 A at 50 days post explosion shows a statistically significant correlation with host HII-region oxygen abundance. The strength of this correlation increases if one excludes abundance measurements derived far from SN explosion sites. The correlation significance also increases if we only analyse a 'gold' IIP sample, and if a colour epoch is used in place of time. In addition, no evidence is found of correlation between progenitor metallicity and SN light-curve or spectral properties - except for that stated above with respect to Fe 5018 A equivalent width - suggesting progenitor metallicity is not a driving factor in producing the diversity observed in our sample. This study provides observational evidence of the usefulness of SNII as metallicity indicators. We finish with a discussion of the methodology needed to use SN spectra as independent metallicity diagnostics throughout the Universe.Comment: Accepted for publication in Astronomy and Astrophyci

The Carnegie Supernova Project I: methods to estimate host-galaxy reddening of stripped-envelope supernovae

We aim to improve upon contemporary methods to estimate host-galaxy reddening of stripped-envelope (SE) supernovae (SNe). To this end the Carnegie Supernova Project (CSP-I) SE SNe photometry data release, consisting of nearly three dozen objects, is used to identify a minimally reddened sub-sample for each traditionally defined spectroscopic sub-types (i.e, SNe~IIb, SNe~Ib, SNe~Ic). Inspection of the optical and near-infrared (NIR) colors and color evolution of the minimally reddened sub-samples reveals a high degree of homogeneity, particularly between 0d to +20d relative to B-band maximum. This motivated the construction of intrinsic color-curve templates, which when compared to the colors of reddened SE SNe, yields an entire suite of optical and NIR color excess measurements. Comparison of optical/optical vs. optical/NIR color excess measurements indicates the majority of the CSP-I SE SNe suffer relatively low amounts of reddening and we find evidence for different R_(V)^(host) values among different SE SN. Fitting the color excess measurements of the seven most reddened objects with the Fitzpatrick (1999) reddening law model provides robust estimates of the host visual-extinction A_(V)^(host) and R_(V)^(host). In the case of the SE SNe with relatively low amounts of reddening, a preferred value of R_(V)^(host) is adopted for each sub-type, resulting in estimates of A_(V)^(host) through Fitzpatrick (1999) reddening law model fits to the observed color excess measurements. Our analysis suggests SE SNe reside in galaxies characterized by a range of dust properties. We also find evidence SNe Ic are more likely to occur in regions characterized by larger R_(V)^(host) values compared to SNe IIb/Ib and they also tend to suffer more extinction. These findings are consistent with work in the literature suggesting SNe Ic tend to occur in regions of on-going star formation.Comment: Abstract abridged to fit allowed limit. Resubmitted to A&A, 34 pages, 19 figures, 6 tables. Constructive comments welcome