1,237 research outputs found
A New Hybrid Framework to Efficiently Model Lines of Sight to Gravitational Lenses
In strong gravitational lens systems, the light bending is usually dominated
by one main galaxy, but may be affected by other mass along the line of sight
(LOS). Shear and convergence can be used to approximate the contributions from
less significant perturbers (e.g. those that are projected far from the lens or
have a small mass), but higher order effects need to be included for objects
that are closer or more massive. We develop a framework for multiplane lensing
that can handle an arbitrary combination of tidal planes treated with shear and
convergence and planes treated exactly (i.e., including higher order terms).
This framework addresses all of the traditional lensing observables including
image positions, fluxes, and time delays to facilitate lens modelling that
includes the non-linear effects due to mass along the LOS. It balances accuracy
(accounting for higher-order terms when necessary) with efficiency (compressing
all other LOS effects into a set of matrices that can be calculated up front
and cached for lens modelling). We identify a generalized multiplane mass sheet
degeneracy, in which the effective shear and convergence are sums over the
lensing planes with specific, redshift-dependent weighting factors.Comment: 13 pages, 2 figure
A Reconciliation between the Consumer Price Index and the Personal Consumption Expenditures Price Index
The Bureau of Labor Statistics (BLS) prepares the Consumer Price Index for All Urban Consumers (CPI-U), and the Bureau of Economic Analysis prepares the Personal Consumption Expenditures (PCE) chain-type price index. Both indexes measure the prices paid by consumers for goods and services. Because the two indexes are based on different underlying concepts, they are constructed differently, and tend to behave differently over time. From the first quarter of 2002 through the second quarter of 2007, the CPI-U increased 0.4 percentage point per year faster than the PCE price index. This paper details and quantifies the differences in growth rates between the CPI-U and the PCE price index; it provides a quarterly reconciliation of growth rates for the 2002:Q1- 2007:Q2 time period. There are several factors that explain the differences in growth rates between the CPI and the PCE price index. First, the indexes are based on difference index-number formulas. The CPI-U is based on a Laspeyres index; the PCE price index is based on a Fisher-Ideal index. Second, the relative weights assigned to the detailed item prices in each index are different because they are based on different data sources. The weights used in the CPIU are based on a household survey, while the weights used in the PCE price index are based on business surveys. Third, there are scope differences between the two indexesâ that is, there are items in the CPI-U that are out-of-scope of the PCE price index, and there are items in the PCE price index that are out-of-scope of the CPI-U. And finally, there are differences in the seasonal-adjustment routines and in the detailed price indexes used to construct the two indexes. Over the 2002:Q1-2007:Q2 time period, this analysis finds that almost half of the 0.4 percentage point difference in growth rates between the CPI-U and the PCE price index was explained by differences in index-number formulas. After adjusting for formula differences, differences in relative weightsâprimarily ârent of shelterââmore than accounted for the remaining difference in growth rates. Net scope differences, in contrast, partly offset the effect of relative weight differences.
Threatened, endemic and harvested â two overlooked European skates
Sandy ray Leucoraja circularis and shagreen ray L. fullonica are large-bodied skate species occurring in the Northeast Atlantic and Mediterranean on the edge of the continental shelf and upper slope. These areas are not sampled effectively by fishery-independent trawl surveys, and fisheries-dependent data are also limited, as these species are landed as a bycatch. Consequently, there are no formal assessments or reference points, even though they are harvested as part of the Total Allowable Catch (TAC) for generic skates and rays. The implementation of data-limited assessment methods is often reliant on robust life-history data, which was lacking. Therefore, biological data were collected from 116 specimens of L. circularis (21â116 cm LT) and 54 specimens of L. fullonica (19â100 cm LT). Length at 50% maturity for L. circularis was estimated at 81 cm LT and 100 cm LT for males and females, respectively. This large size at maturity makes them more biologically vulnerable than other skate species managed under the generic TAC. This inherent vulnerability, low representation of mature individuals in trawl surveys and bycatch risk due to spatial overlap with important commercial fisheries suggests that both species, assessed as Threatened, would benefit from precautionary species-specific management measures. L. circularis and L. fullonica are respectively, the only IUCN listed Endangered and Vulnerable elasmobranchs that are endemic to Europe and also occur in UK waters. Therefore, with the eastern Atlantic being the main part of their distribution, urgent research and management action is of even greater importance to conserve them
Comprehensive Observations of the Bright and Energetic Type Iax SN 2012Z: Interpretation as a Chandrasekhar Mass White Dwarf Explosion
We present UV through NIR broad-band photometry, and optical and NIR
spectroscopy of Type Iax supernova 2012Z. The data set consists of both early
and late-time observations, including the first late phase NIR spectrum
obtained for a spectroscopically classified SN Iax. Simple model calculations
of its bolometric light curve suggest SN 2012Z produced ~0.3 M_sun of (56)Ni,
ejected about a Chandrasekhar mass of material, and had an explosion energy of
~10^51 erg, making it one of the brightest and most energetic SN Iax yet
observed. The late phase NIR spectrum of SN 2012Z is found to broadly resemble
similar epoch spectra of normal SNe Ia; however, like other SNe Iax,
corresponding visual-wavelength spectra differ substantially compared to all
supernova types. Constraints from the distribution of IMEs, e.g. silicon and
magnesium, indicate that the outer ejecta did not experience significant mixing
during or after burning, and the late phase NIR line profiles suggests most of
the (56)Ni is produced during high density burning. The various observational
properties of SN 2012Z are found to be consistent with the theoretical
expectations of a Chandrasekhar mass white dwarf progenitor that experiences a
pulsational delayed detonation, which produced several tenths of a solar mass
of (56)Ni during the deflagration burning phase and little (or no) (56)Ni
during the detonation phase. Within this scenario only a moderate amount of
Rayleigh-Taylor mixing occurs both during the deflagration and fallback phase
of the pulsation, and the layered structure of the IMEs is a product of the
subsequent denotation phase. The fact that the SNe Iax population does not
follow a tight brightness-decline relation similar to SNe Ia can then be
understood in the framework of variable amounts of mixing during pulsational
rebound and variable amounts of (56)Ni production during the early subsonic
phase of expansion.Comment: Submitted to A&A, manuscript includes response to referee's comments.
39 pages, including 16 figures, 9 table
AT 2017be - a new member of the class of Intermediate-Luminosity Red Transients
We report the results of our spectrophotometric monitoring campaign for
AT~2017be in NGC~2537. Its lightcurve reveals a fast rise to an optical
maximum, followed by a plateau lasting about 30 days, and finally a fast
decline. Its absolute peak magnitude ( 12 ) is
fainter than that of core-collapse supernovae, and is consistent with those of
supernova impostors and other Intermediate-Luminosity Optical Transients. The
quasi-bolometric lightcurve peaks at 2 10 erg s,
and the late-time photometry allows us to constrain an ejected Ni mass
of 8 10\msun. The spectra of AT~2017be show minor
evolution over the observational period, a relatively blue continuum showing at
early phases, which becomes redder with time. A prominent H emission
line always dominates over other Balmer lines. Weak Fe {\sc ii} features,
Ca~{\sc ii} HK and the Ca {\sc ii} NIR triplet are also visible, while
P-Cygni absorption troughs are found in a high resolution spectrum. In
addition, the [Ca~{\sc ii}] 7291,7324 doublet is visible in all
spectra. This feature is typical of Intermediate-Luminosity Red Transients
(ILRTs), similar to SN~2008S. The relatively shallow archival Spitzer data are
not particularly constraining. On the other hand, a non-detection in deeper
near-infrared HST images disfavours a massive Luminous Blue Variable eruption
as the origin for AT~2017be. As has been suggested for other ILRTs, we propose
that AT~2017be is a candidate for a weak electron-capture supernova explosion
of a super-asymptotic giant branch star, still embedded in a thick dusty
envelope.Comment: 21 pages, 15 figures, accepted by MNRA
SN Refsdal: Classification as a Luminous and Blue SN 1987A-like Type II Supernova
We have acquired Hubble Space Telescope (HST) and Very Large Telescope
near-infrared spectra and images of supernova (SN) Refsdal after its discovery
as an Einstein cross in Fall 2014. The HST light curve of SN Refsdal matches
the distinctive, slowly rising light curves of SN 1987A-like supernovae (SNe),
and we find strong evidence for a broad H-alpha P-Cygni profile in the HST
grism spectrum at the redshift (z = 1.49) of the spiral host galaxy. SNe IIn,
powered by circumstellar interaction, could provide a good match to the light
curve of SN Refsdal, but the spectrum of a SN IIn would not show broad and
strong H-alpha absorption. From the grism spectrum, we measure an H-alpha
expansion velocity consistent with those of SN 1987A-like SNe at a similar
phase. The luminosity, evolution, and Gaussian profile of the H-alpha emission
of the WFC3 and X-shooter spectra, separated by ~2.5 months in the rest frame,
provide additional evidence that supports the SN 1987A-like classification. In
comparison with other examples of SN 1987A-like SNe, SN Refsdal has a blue B-V
color and a high luminosity for the assumed range of potential magnifications.
If SN Refsdal can be modeled as a scaled version of SN 1987A, we estimate it
would have an ejecta mass of 20+-5 solar masses. The evolution of the light
curve at late times will provide additional evidence about the potential
existence of any substantial circumstellar material (CSM). Using MOSFIRE and
X-shooter spectra, we estimate a subsolar host-galaxy metallicity (8.3+-0.1 dex
and <8.4 dex, respectively) near the explosion site.Comment: Submitted to ApJ; 26 page
- âŠ