From outside of ethics: Moss, Sarah. Probabilistic Knowledge

Book Review published in the From Outside of Ethics section of Ethics: An International Journal of Social, Political, and Legal Philosophy. Moss, Sarah. Probabilistic Knowledge. Oxford: Oxford University Press, 2018. Pp. 288. $54.00 (cloth)

Detecting the progenitors of core collapse supernovae

The masses and the evolutionary states of the progenitors of core-collapse supernovae are not well constrained by direct observations. Stellar evolution theory generally predicts that massive stars with initial masses less than about 30M_sol should undergo core-collapse when they are cool M-type supergiants. However the only two detections of a SN progenitor before explosion are SN1987A and SN1993J, and neither of these was an M-type supergiant. Attempting to identify the progenitors of supernovae is a difficult task, as precisely predicting the time of explosion of a massive star is impossible for obvious reasons. There are several different types of supernovae which have different spectral and photometric evolution, and how exactly these are related to the evolutionary states of the progenitor stars is not currently known. I will describe a novel project which may allow the direct identification of core-collapse supernovae progenitors on pre-explosion images of resolved, nearby galaxies. This project is now possible with the excellent image archives maintained by several facilities and will be enhanced by the new initiatives to create Virtual Observatories, the earliest of which ASTROVIRTEL is already producing results.Comment: To appear in the Euroconference proceedings of "The Evolution of Galaxies II. Basic Building Blocks", held in La Renunion, October 2001, eds. M. Sauvage, et al., 5 pages inc. 2 figs, (Kluwer

The Progenitor of SN 2005cs in the Whirlpool Galaxy

The progenitor of SN 2005cs, in the galaxy M51, is identified in pre-explosion HST ACS WFC imaging. Differential astrometry, with post-explosion ACS HRC F555W images, permitted the identification of the progenitor with an accuracy of 0.006". The progenitor was detected in the F814W pre-explosion image with I=23.3+/-0.2, but was below the detection thresholds of the F435W and F555W images, with B<24.8 and V<25 at 5-sigma. Limits were also placed on the U and R band fluxes of the progenitor from pre-explosion HST WFPC2 F336W and F675W images. Deep images in the infra-red from NIRI on the Gemini-North telescope were taken 2 months prior to explosion, but the progenitor is not clearly detected on these. The upper limits for the JHK magnitudes of the progenitor were J<21.9,H<21.1 and K<20.7. Despite having a detection in only one band, a restrictive spectral energy distribution of the progenitor star can be constructed and a robust case is made that the progenitor was a red supergiant with spectral type between mid-K to late-M. The spectral energy distribution allows a region in the theoretical HR diagram to be determined which must contain the progenitor star. The initial mass of the star is constrained to be M(ZAMS)=9+3/-2 M_solar, which is very similar to the identified progenitor of the type II-P SN 2003gd, and also consistent with upper mass limits placed on five other similar SNe. The upper limit in the deep K-band image is significant in that it allows us to rule out the possibility that the progenitor was a significantly higher mass object enshrouded in a dust cocoon before core-collapse. This is further evidence that the trend for type II-P SNe to arise in low to moderate mass red supergiants is real.Comment: Accepted (31/08/05) for publication in MNRAS Letter

Observational constraints on the progenitors of core-collapse supernovae : the case for missing high mass stars

Over the last 15 years, the supernova community has endeavoured to identify progenitor stars of core-collapse supernovae in high resolution archival images of their galaxies.This review compiles results (from 1999 - 2013) in a distance limited sample and discusses the implications. The vast majority of the detections of progenitor stars are of type II-P, II-L or IIb with one type Ib progenitor system detected and many more upper limits for progenitors of Ibc supernovae (14). The data for these 45 supernovae progenitors illustrate a remarkable deficit of high luminosity stars above an apparent limit of Log L ~= 5.1 dex. For a typical Salpeter IMF, one would expect to have found 13 high luminosity and high mass progenitors. There is, possibly, only one object in this time and volume limited sample that is unambiguously high mass (the progenitor of SN2009ip). The possible biases due to the influence of circumstellar dust and sample selection methods are reviewed. It does not appear likely that these can explain the missing high mass progenitor stars. This review concludes that the observed populations of supernovae in the local Universe are not, on the whole, produced by high mass (M > ~18Msun) stars. Theoretical explosions of model stars also predict that black hole formation and failed supernovae tend to occur above M > ~18Msun. The models also suggest there are islands of explodability for stars in the 8-120Msun range. The observational constraints are quite consistent with the bulk of stars above M > ~18Msun collapsing to form black holes with no visible supernovae. (Abridged).Comment: Invited review article for Publications of the Astronomical Society of Australia, to be published in a special PASA collection on "SN1987A and Supernovae in the Local Universe". This is the accepted version, after referee review. Additional minor corrections to match proofs. (25 pages

Super Luminous Supernovae as standardizable candles and high redshift distance probes

We investigate the use of type Ic Super Luminous Supernovae as standardizable candles and distance indicators. Their appeal as cosmological probes stems from their remarkable peak luminosities, hot blackbody temperatures and bright restframe ultraviolet emission. We present a sample of sixteen published SLSN, from redshifts 0.1 to 1.2 and calculate accurate K-corrections to determine uniform magnitudes in two synthetic rest-frame filters with central wavelengths at 400nm and 520nm. At 400nm, we find a low scatter in their uncorrected, raw mean magnitudes with M(400)=-21.70 for the full sample of sixteen objects. We investigate the correlation between their decline rates and peak magnitude and find that the brighter events appear to decline more slowly. We define a $\Delta M(30)$ decay relation. This correlates peak magnitude and decline over 30 days and can reduce the scatter to 0.25. We further show that M(400) appears to have a strong colour dependence. Using this colour rate decay relation, a low scatter of between 0.19 and 0.26 can be found depending on sample selection. However we caution that only eight to ten objects currently have enough data to test this colour rate decline relation. We conclude that SLSN Ic are promising distance indicators at high redshift in regimes beyond those possible with SNe Ia. Although the empirical relationships are encouraging, the unknown progenitor systems and how they may evolve with redshift are of some concern. The two major measurement uncertainties are the limited numbers of low redshift objects to test these relationships and internal dust extinction in the host galaxies.Comment: The authors regret that in the published version (2014, APJ, 796, 87) there were calculation errors in many of the values in Table 1 and in particular the important values for M(400) and the decline rates. The two main conclusions of the paper are unchanged, but the quantitative rms values are larger than previously reporte

Chemical composition of B-type supergiants in the OB8, OB10, OB48, OB78 associations of M31

Absolute and differential chemical abundances are presented for the largest group of massive stars in M31 studied to date. These results were derived from intermediate resolution spectra of seven B-type supergiants, lying within four OB associations covering a galactocentric distance of 5 - 12 kpc. The results are mainly based on an LTE analysis, and we additionally present a full non-LTE, unified model atmosphere analysis of one star (OB78-277) to demonstrate the reliability of the differential LTE technique. A comparison of the stellar oxygen abundance with that of previous nebular results shows that there is an offset of between ~0.15 - 0.4 dex between the two methods which is critically dependent on the empirical calibration adopted for the R23 parameter with [O/H]. However within the typical errors of the stellar and nebular analyses (and given the strength of dependence of the nebular results on the calibration used) the oxygen abundances determined in each method are fairly consistent. We determine the radial oxygen abundance gradient from these stars, and do not detect any systematic gradient across this galactocentric range. We find that the inner regions of M31 are not, as previously thought, very 'metal rich'. Our abundances of C, N, O, Mg, Si, Al, S and Fe in the M31 supergiants are very similar to those of massive stars in the solar neighbourhood.Comment: 15 pages, 9 figures and 9 tables. Submitted to A&A April 200

Loop interaction in the visible emission corona: Morphological details

Coronagraph observations of two post flare loop systems, recorded photographically in the emissions of Fe 14 (5303 A) and Fe 10 (6374 A), show occasional enhancements at the intersections of some loops. The brightness of such enhancements in the green line gradually increases to a maximum value several times greater than that of the legs of the loops and then declines with a typical lifetime approx. 30 to 60 min. In red line emission the loop systems are usually very faint, but show the same overall type of enhancement, with a lag in maximum brightness relative to that of the green line approx. 10 min. The electron density, derived from the cooling time, is approx. 10 to the 12th power/cu cm

Effects of Water Column P-availability and Litter Microbial Mediated Processes and Stoichiometry in Aquatic Systems

Anthropogenic nutrient enrichment of aquatic ecosystems is prevalent and can have detrimental effects on biological condition. Many of these effects have been attributed directly or indirectly to changes in autotrophic processes. However, in detrital-based streams changes in course detrital stoichiometry and decomposition have been related to changes community structure and production at higher trophic levels highlighting the importance of considering the heterotrophic microbial responses to enrichment. Leaf litter stoichiometry, which is determined in part by the tree species source and the microbial communities that comprise the associated biofilm, is likely related to decomposition rates, but few studies examine these variables in combination across a nutrient concentration gradient. Dissolved inorganic phosphorus (DIP) (0, 10, 25, 50, 75, 100, 250, 500, 1000, 2000 µg/L DIP) and litter type (sugar maple and post oak) were manipulated in a 210 day laboratory microcosm study to determine their effect on litter C:P and decomposition rates and to examine their effects on short duration measures of respiration and alkaline phosphatase activity (APA) taken on several dates spanning the decomposition process. I found that C:P declined and decomposition rates increased in a saturating relationship along the DIP gradient indicating P-limitation of decomposition at low DIP concentrations. Saturation values for maple and oak C:P and decomposition rates were 500 and 830 and 0.0085 + 0.0005 and 0.0029 + 0.0002, respectively. Litter C:P saturation DIP concentrations saturated at approximately 80 µg/L for both litter types, while decomposition rates saturated at less than 25 µg/L for both litter types. APA and respiration rates were not correlated, but positive correlations were found between C:P and APA on several days (range in r = 0.568-0.670, p\u3c0.008). Positive correlations between respiration rates and decomposition across several days but explained little variation in decomposition rate (r\u3c0.5) Maple tended to have greater APA and respiration relative to oak litter, though not always statistically. These results demonstrate that litter type and DIP concentration are both important factors affecting litter stoichiometry and quantity in detrital systems, but do not support the use of APA and respiration as instantaneous measures of limitation of decomposition in streams. I provide insight into the complexity of the dynamics of nutrient enrichment in stream, educating potential impacts of nutrient loading on aquatic ecosystems

The Disappearance of the Progenitors of Supernovae 1993J and 2003gd

Using images from the Hubble Space Telescope (HST) and the Gemini Telescope we confirm the disappearance of the progenitors of two Type II supernovae (SNe), and evaluate the presence of other stars associated with them. We find that the progenitor of SN 2003gd, an M-supergiant star, is no longer observed at the SN location, and determine its intrinsic brightness using image subtraction techniques. The progenitor of SN 1993J, a K-supergiant star, is also no longer present, but its B-supergiant binary companion is still observed. The disappearance of the progenitors confirms that these two SNe were produced by Red Supergiants.Comment: Science, in press, published online 19/03/09, 28 pages (MS+SOM) (high-res figures available at http://www.dark-cosmology.dk/~justyn/research/