arXiv subjects

W. S. Burgett

Publications and source records attributed to W. S. Burgett.

At least 19 recordsLinked to original sources

arXiv2019

The Pan-STARRS1 Surveys

Pan-STARRS1 has carried out a set of distinct synoptic imaging sky surveys including the $3π$ Steradian Survey and the Medium Deep Survey in 5 bands ($grizy_{P1}$). The mean 5$σ$ point source limiting sensitivities in the stacked 3$π$ Steradian Survey in $grizy_{P1}$ are (23.3, 23.2, 23.1, 22.3, 21.4) respectively. The upper bound on the systematic uncertainty in the photometric calibration across the sky is 7-12 millimag depending on the bandpass. The systematic uncertainty of the astrometric calibration using the Gaia frame comes from a comparison of the results with Gaia: the standard deviation of the mean and median residuals ($ Δra, Δdec $) are (2.3, 1.7) milliarcsec, and (3.1, 4.8) milliarcsec respectively. The Pan-STARRS system and the design of the PS1 surveys are described and an overview of the resulting image and catalog data products and their basic characteristics are described together with a summary of important results. The images, reduced data products, and derived data products from the Pan-STARRS1 surveys are available to the community from the Mikulski Archive for Space Telescopes (MAST) at STScI.

astro-ph.IM↗

arXiv2019

Pan-STARRS Pixel Processing: Detrending, Warping, Stacking

The Pan-STARRS1 Science Consortium have carried out a set of imaging surveys using the 1.4 giga-pixel GPC1 camera on the PS1 telescope. As this camera is composed of many individual electronic readouts, and covers a very large field of view, great care was taken to ensure that the many instrumental effects were corrected to produce the most uniform detector response possible. We present the image detrending steps used as part of the processing of the data contained within the public release of the Pan-STARRS1 Data Release 1 (DR1). In addition to the single image processing, the methods used to transform the 375,573 individual exposures into a common sky-oriented grid are discussed, as well as those used to produce both the image stack and difference combination products.

astro-ph.IM↗

arXiv2018

Cepheids in M31 - The PAndromeda Cepheid sample

We present the largest Cepheid sample in M31 based on the complete Pan-STARRS1 survey of Andromeda (PAndromeda) in the $r_{\mathrm{P1}}$ , $i_{\mathrm{P1}}$ and $g_{\mathrm{P1}}$ bands. We find 2686 Cepheids with 1662 fundamental mode Cepheids, 307 first-overtone Cepheids, 278 type II Cepheids and 439 Cepheids with undetermined Cepheid type. Using the method developed by Kodric et al. (2013) we identify Cepheids by using a three dimensional parameter space of Fourier parameters of the Cepheid light curves combined with a color cut and other selection criteria. This is an unbiased approach to identify Cepheids and results in a homogeneous Cepheid sample. The Period-Luminosity relations obtained for our sample have smaller dispersions than in our previous work. We find a broken slope that we previously observed with HST data in Kodric et al. (2015), albeit with a lower significance.

astro-ph.GA↗

arXiv2018

The Complete Light-curve Sample of Spectroscopically Confirmed Type Ia Supernovae from Pan-STARRS1 and Cosmological Constraints from The Combined Pantheon Sample

We present optical light curves, redshifts, and classifications for 365 spectroscopically confirmed Type Ia supernovae (SNe Ia) discovered by the Pan-STARRS1 (PS1) Medium Deep Survey. We detail improvements to the PS1 SN photometry, astrometry and calibration that reduce the systematic uncertainties in the PS1 SN Ia distances. We combine the subset of 279 PS1 SN Ia ($0.03 < z < 0.68$) with useful distance estimates of SN Ia from SDSS, SNLS, various low-z and HST samples to form the largest combined sample of SN Ia consisting of a total of 1048 SN Ia ranging from $0.01 < z < 2.3$, which we call the `Pantheon Sample'. When combining Planck 2015 CMB measurements with the Pantheon SN sample, we find $Ω_m=0.307\pm0.012$ and $w = -1.026\pm0.041$ for the wCDM model. When the SN and CMB constraints are combined with constraints from BAO and local H0 measurements, the analysis yields the most precise measurement of dark energy to date: $w0 = -1.007\pm 0.089$ and $wa = -0.222 \pm0.407$ for the w0waCDM model. Tension with a cosmological constant previously seen in an analysis of PS1 and low-z SNe has diminished after an increase of $2\times$ in the statistics of the PS1 sample, improved calibration and photometry, and stricter light-curve quality cuts. We find the systematic uncertainties in our measurements of dark energy are almost as large as the statistical uncertainties, primarily due to limitations of modeling the low-redshift sample. This must be addressed for future progress in using SN Ia to measure dark energy.

astro-ph.CO↗

arXiv2018

Measuring Dark Energy Properties with Photometrically Classified Pan-STARRS Supernovae. II. Cosmological Parameters

We use 1169 Pan-STARRS supernovae (SNe) and 195 low-$z$ ($z < 0.1$) SNe Ia to measure cosmological parameters. Though most Pan-STARRS SNe lack spectroscopic classifications, in a previous paper (I) we demonstrated that photometrically classified SNe can be used to infer unbiased cosmological parameters by using a Bayesian methodology that marginalizes over core-collapse (CC) SN contamination. Our sample contains nearly twice as many SNe as the largest previous SN Ia compilation. Combining SNe with Cosmic Microwave Background (CMB) constraints from Planck, we measure the dark energy equation of state parameter $w$ to be -0.989$\pm$0.057 (stat$+$sys). If $w$ evolves with redshift as $w(a) = w_0 + w_a(1-a)$, we find $w_0 = -0.912 \pm 0.149$ and $w_a =$ -0.513$\pm$0.826. These results are consistent with cosmological parameters from the Joint Lightcurve Analysis and the Pantheon sample. We try four different photometric classification priors for Pan-STARRS SNe and two alternate ways of modeling CC SN contamination, finding that no variant gives a $w$ differing by more than 2% from the baseline measurement. The systematic uncertainty on $w$ due to marginalizing over CC SN contamination, $σ_w^{\textrm{CC}} = 0.012$, is the third-smallest source of systematic uncertainty in this work. We find limited (1.6$σ$) evidence for evolution of the SN color-luminosity relation with redshift, a possible systematic that could constitute a significant uncertainty in future high-$z$ analyses. Our data provide one of the best current constraints on $w$, demonstrating that samples with $\sim$5% CC SN contamination can give competitive cosmological constraints when the contaminating distribution is marginalized over in a Bayesian framework.

astro-ph.CO↗

arXiv2017

Photometry and Proper Motions of M, L, and T Dwarfs from the Pan-STARRS1 3$π$ Survey

We present a catalog of 9888 M, L and T dwarfs detected in the Pan-STARRS1 3$π$ Survey (PS1), covering three-quarters of the sky. Our catalog contains nearly all known objects of spectral types L0-T2 in the PS1 field, with objects as early as M0 and as late as T9, and includes PS1, 2MASS, AllWISE, and Gaia DR1 photometry. We analyze the different types of photometry reported by PS1, and use two types in our catalog to maximize both depth and accuracy. Using parallaxes from the literature, we construct empirical SEDs for field ultracool dwarfs spanning 0.5-12 $μ$m. We determine typical colors of M0-T9 dwarfs, and we highlight the distinctive colors of subdwarfs and young objects. Our catalog includes 492 L dwarfs detected in $r_{\rm P1}$, the largest sample of L dwarfs detected at such blue wavelengths. We combine astrometry from PS1, 2MASS, and Gaia DR1 to calculate new proper motions for our catalog. We achieve a median precision of 2.9 mas yr$^{-1}$, a factor of $\approx$3-10 improvement over previous large catalogs. Our catalog contains proper motions for 2405 M6-T9 dwarfs and includes the largest set of homogeneous proper motions for L and T dwarfs published to date, 406 objects for which there were no previous measurements, and 1176 objects for which we improve upon previous literature values. We analyze the kinematics of ultracool dwarfs in our catalog and find evidence that bluer but otherwise generic late-M and L field dwarfs (i.e., not subdwarfs) tend to have higher tangential velocities compared to typical field objects. With the public release of the PS1 data, this survey will continue to be an essential tool for characterizing the ultracool dwarf population.

astro-ph.SR↗

arXiv2017

An updated Type II supernova Hubble diagram

We present photometry and spectroscopy of nine Type II-P/L supernovae (SNe) with redshifts in the 0.045 < z < 0.335 range, with a view to re-examining their utility as distance indicators. Specifically, we apply the expanding photosphere method (EPM) and the standardized candle method (SCM) to each target, and find that both methods yield distances that are in reasonable agreement with each other. The current record-holder for the highest-redshift spectroscopically confirmed SN II-P is PS1-13bni (z = 0.335 +0.009 -0.012), and illustrates the promise of Type II SNe as cosmological tools. We updated existing EPM and SCM Hubble diagrams by adding our sample to those previously published. Within the context of Type II SN distance measuring techniques, we investigated two related questions. First, we explored the possibility of utilising spectral lines other than the traditionally used Fe II 5169 to infer the photospheric velocity of SN ejecta. Using local well-observed objects, we derive an epoch-dependent relation between the strong Balmer line and Fe II 5169 velocities that is applicable 30 to 40 days post-explosion. Motivated in part by the continuum of key observables such as rise time and decline rates exhibited from II-P to II-L SNe, we assessed the possibility of using Hubble-flow Type II-L SNe as distance indicators. These yield similar distances as the Type II-P SNe. Although these initial results are encouraging, a significantly larger sample of SNe II-L would be required to draw definitive conclusions.

astro-ph.CO↗

arXiv2017

Charge Diffusion Variations in Pan-STARRS\,1 CCDs

Thick back-illuminated deep-depletion CCDs have superior quantum efficiency over previous generations of thinned and traditional thick CCDs. As a result, they are being used for wide-field imaging cameras in several major projects. We use observations from the Pan-STARRS $3π$ survey to characterize the behavior of the deep-depletion devices used in the Pan-STARRS1 Gigapixel Camera. We have identified systematic spatial variations in the photometric measurements and stellar profiles which are similar in pattern to the so-called "tree rings" identified in devices used by other wide-field cameras (e.g., DECam and Hypersuprime Camera). The tree-ring features identified in these other cameras result from lateral electric fields which displace the electrons as they are transported in the silicon to the pixel location. In contrast, we show that the photometric and morphological modifications observed in the GPC1 detectors are caused by variations in the vertical charge transportation rate and resulting charge diffusion variations.

astro-ph.IM↗

arXiv2017

The Pan-STARRS1 Medium-deep Survey: Star Formation Quenching in Group and Cluster Environments

We make use of a catalog of 1600 Pan-STARRS1 groups produced by the probability friends-of-friends algorithm to explore how the galaxy properties, i.e. the specific star formation rate (SSFR) and quiescent fraction, depend on stellar mass and group-centric radius. The work is the extension of Lin et al. (2014). In this work, powered by a stacking technique plus a background subtraction for contamination removal, a finer correction and more precise results are obtained than in our previous work. We find that while the quiescent fraction increases with decreasing group-centric radius the median SSFRs of star-forming galaxies in groups at fixed stellar mass drop slightly from the field toward the group center. This suggests that the major quenching process in groups is likely a fast mechanism. On the other hand, a reduction in SSFRs by ~0.2 dex is seen inside clusters as opposed to the field galaxies. If the reduction is attributed to the slow quenching effect, the slow quenching process acts dominantly in clusters. In addition, we also examine the density-color relation, where the density is defined by using a sixth-nearest neighbor approach. Comparing the quiescent fractions contributed from the density and radial effect, we find that the density effect dominates over the massive group or cluster galaxies, and the radial effect becomes more effective in less massive galaxies. The results support mergers and/or starvation as the main quenching mechanisms in the group environment, while harassment and/or starvation dominate in clusters.

astro-ph.GA↗

arXiv2017

Measuring the Properties of Dark Energy with Photometrically Classified Pan-STARRS Supernovae. I. Systematic Uncertainty from Core-Collapse Supernova Contamination

The Pan-STARRS (PS1) Medium Deep Survey discovered over 5,000 likely supernovae (SNe) but obtained spectral classifications for just 10% of its SN candidates. We measured spectroscopic host galaxy redshifts for 3,147 of these likely SNe and estimate that $\sim$1,000 are Type Ia SNe (SNe Ia) with light-curve quality sufficient for a cosmological analysis. We use these data with simulations to determine the impact of core-collapse SN (CC SN) contamination on measurements of the dark energy equation of state parameter, $w$. Using the method of Bayesian Estimation Applied to Multiple Species (BEAMS), distances to SNe Ia and the contaminating CC SN distribution are simultaneously determined. We test light-curve based SN classification priors for BEAMS as well as a new classification method that relies upon host galaxy spectra and the association of SN type with host type. By testing several SN classification methods and CC SN parameterizations on large SN simulations, we estimate that CC SN contamination gives a systematic error on $w$ ($σ_w^{CC}$) of 0.014, 29% of the statistical uncertainty. Our best method gives $σ_w^{CC} = 0.004$, just 8% of the statistical uncertainty, but could be affected by incomplete knowledge of the CC SN distribution. This method determines the SALT2 color and shape coefficients, $α$ and $β$, with $\sim$3% bias. However, we find that some variants require $α$ and $β$ to be fixed to known values for BEAMS to yield accurate measurements of $w$. Finally, the inferred abundance of bright CC SNe in our sample is greater than expected based on measured CC SN rates and luminosity functions.

astro-ph.CO↗

arXiv2017

A Search for L/T Transition Dwarfs With Pan-STARRS1 and WISE. III. Young L Dwarf Discoveries and Proper Motion Catalogs in Taurus and Scorpius-Centaurus

We present the discovery of eight young M7-L2 dwarfs in the Taurus star-forming region and the Scorpius-Centaurus OB Association, serendipitously found during a wide-field search for L/T transition dwarfs using Pan-STARRS1 (optical) and WISE (mid-infrared) photometry. We identify PSO J060.3200+25.9644 (near-infrared spectral type L1) and PSO J077.1033+24.3809 (L2) as new members of Taurus based on their VL-G gravity classifications, the consistency of their photometry and proper motions with previously known Taurus objects, and the low probability of contamination by field objects. PSO J077.1033+24.3809 is the coolest substellar member of Taurus found to date. Both Taurus objects are among the lowest mass free-floating objects ever discovered, with estimated masses $\approx$6 M$_{\rm Jup}$, and provide further evidence that isolated planetary-mass objects can form as part of normal star-formation processes. PSO J060.3200+25.9644 (a.k.a. DANCe J040116.80+255752.2) was previously identified as a likely member of the Pleiades (age $\approx125$ Myr) based on photometry and astrometry, but its VL-G gravity classification and near-infrared photometry imply a much younger age and thus point to Taurus membership. We have also discovered six M7-L1 dwarfs in outlying regions of Scorpius-Centaurus with photometry, proper motions, and low-gravity spectral signatures consistent with membership. These objects have estimated masses $\approx$15-36 M$_{\rm Jup}$. The M7 dwarf, PSO J237.1470-23.1489, shows excess mid-infrared flux implying the presence of a circumstellar disk. Finally, we present catalogs of Pan-STARRS1 proper motions for low-mass members of Taurus and Upper Scorpius with median precisions of $\approx$3 mas yr$^{-1}$, including 67 objects with no previous proper motion and 359 measurements that improve on literature values.

astro-ph.SR↗

arXiv2017

2MASS 0213+3648 C: A wide T3 benchmark companion to an an active, old M dwarf binary

We present the discovery of a 360 AU separation T3 companion to the tight (3.1 AU) M4.5+M6.5 binary 2MASS J02132062+3648506. This companion was identified using Pan-STARRS1 data and, despite its relative proximity to the Sun (22.2$_{-4.0}^{+6.4}$ pc; Pan-STARRS1 parallax) and brightness ($J$=15.3), appears to have been missed by previous studies due to its position near a diffraction spike in 2MASS. The close M~dwarf binary has active X-ray and H$α$ emission and shows evidence for UV flares. The binary's weak {\it GALEX} UV emission and strong Na I 8200ÅNa absorption leads us to an age range of $\sim$1-10Gyr. Applying this age range to evolutionary models implies the wide companion has a mass of 0.063$\pm$0.009\,$M_{\odot}$. 2MASS J0213+3648 C provides a relatively old benchmark close to the L/T transition and acts as a key, older comparison to the much younger early-T companions HN~Peg~B and GU~Psc~b.

astro-ph.SR↗

arXiv2016

Detection of Time Lags Between Quasar Continuum Emission Bands based on Pan-STARRS Light-curves

We study the time lags between the continuum emission of quasars at different wavelengths, based on more than four years of multi-band ($g$, $r$, $i$, $z$) light-curves in the Pan-STARRS Medium Deep Fields. As photons from different bands emerge from different radial ranges in the accretion disk, the lags constrain the sizes of the accretion disks. We select 240 quasars with redshifts $z \approx 1$ or $z \approx 0.3$ that are relatively emission line free. The light curves are sampled from day to month timescales, which makes it possible to detect lags on the scale of the light crossing time of the accretion disks. With the code JAVELIN, we detect typical lags of several days in the rest frame between the $g$ band and the $riz$ bands. The detected lags are $\sim 2-3$ times larger than the light crossing time estimated from the standard thin disk model, consistent with the recently measured lag in NGC5548 and micro-lensing measurements of quasars. The lags in our sample are found to increase with increasing luminosity. Furthermore, the increase in lags going from $g-r$ to $g-i$ and then to $g-z$ is slower than predicted in the thin disk model, particularly for high luminosity quasars. The radial temperature profile in the disk must be different from what is assumed. We also find evidence that the lags decrease with increasing line ratios between ultraviolet FeII lines and MgII, which may point to changes in the accretion disk structure at higher metallicity.

astro-ph.HE↗

arXiv2016

A Search for L/T Transition Dwarfs With Pan-STARRS1 and WISE. II. L/T Transition Atmospheres and Young Discoveries

The evolution of brown dwarfs from L to T spectral types is one of the least understood aspects of the ultracool population, partly for lack of a large, well-defined, and well-characterized sample in the L/T transition. To improve the existing census, we have searched $\approx$28,000 deg$^2$ using the Pan-STARRS1 and WISE surveys for L/T transition dwarfs within 25 pc. We present 130 ultracool dwarf discoveries with estimated distances $\approx9-130$ pc, including 21 that were independently discovered by other authors and 3 that were previously identified as photometric candidates. Seventy-nine of our objects have near-IR spectral types of L6-T4.5, the most L/T transition dwarfs from any search to date, and we have increased the census of L9-T1.5 objects within 25 pc by over 50%. The color distribution of our discoveries provides further evidence for the "L/T gap," a deficit of objects with $(J-K)_{\rm MKO}\approx0.0-0.5$ mag in the L/T transition, and thus reinforces the idea that the transition from cloudy to clear photospheres occurs rapidly. Among our discoveries are 31 candidate binaries based on their low-resolution spectral features. Two of these candidates are common proper motion companions to nearby main sequence stars; if confirmed as binaries, these would be rare benchmark systems with the potential to stringently test ultracool evolutionary models. Our search also serendipitously identified 23 late-M and L dwarfs with spectroscopic signs of low gravity implying youth. Finally, we identify 10 candidate members of nearby young moving groups (YMG) with spectral types L7-T4.5, including three showing spectroscopic signs of low gravity. If confirmed, any of these would be among the coolest known YMG members and would help to determine the effective temperature at which young brown dwarfs cross the L/T transition. (Abridged)

astro-ph.SR↗

arXiv2016

Hiding in Plain Sight - Recovering Clusters of Galaxies with the Strongest AGN in Their Cores

A key challenge in understanding the feedback mechanism of AGN in Brightest Cluster Galaxies (BCGs) is the inherent rarity of catching an AGN during its strong outburst phase. This is exacerbated by the ambiguity of differentiating between AGN and clusters in X-ray observations. If there is evidence for an AGN then the X-ray emission is commonly assumed to be dominated by the AGN emission, introducing a selection effect against the detection of AGN in BCGs. In order to recover these 'missing' clusters, we systematically investigate the colour-magnitude relation around some ~3500 ROSAT All Sky Survey selected AGN, looking for signs of a cluster red sequence. Amongst our 22 candidate systems, we independently rediscover several confirmed systems, where a strong AGN resides in a central galaxy. We compare the X-ray luminosity to red sequence richness distribution of our AGN candidate systems with that of a similarly selected comparison sample of ~1000 confirmed clusters and identify seven 'best' candidates (all of which are BL Lac objects), where the X-ray flux is likely to be a comparable mix between cluster and AGN emission. We confirm that the colours of the red sequence are consistent with the redshift of the AGN, that the colours of the AGN host galaxy are consistent with AGN, and, by comparing their luminosities with those from our comparison clusters, confirm that the AGN hosts are consistent with BCGs.

astro-ph.GA↗

arXiv2016

Slowly fading super-luminous supernovae that are not pair-instability explosions

Super-luminous supernovae that radiate more than 10^44 ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1-4. Some evolve slowly, resembling models of 'pair-instability' supernovae. Such models involve stars with original masses 140-260 times that of the Sun that now have carbon-oxygen cores of 65-30 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron-positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of 56Ni are synthesized; this isotope decays to 56Fe via 56Co, powering bright light curves. Such massive progenitors are expected to have formed from metal-poor gas in the early Universe. Recently, supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after the Big Bang) with a metallicity one-third that of the Sun was observed to look like a fading pair-instability supernova. Here we report observations of two slow-to-fade super-luminous supernovae that show relatively fast rise times and blue colours, which are incompatible with pair-instability models. Their late-time light-curve and spectral similarities to supernova 2007bi call the nature of that event into question. Our early spectra closely resemble typical fast-declining super-luminous supernovae, which are not powered by radioactivity. Modelling our observations with 10-16 solar masses of magnetar-energized ejecta demonstrates the possibility of a common explosion mechanism. The lack of unambiguous nearby pair-instability events suggests that their local rate of occurrence is less than 6x10^-6 times that of the core-collapse rate.

astro-ph.CO↗

arXiv2016

Dust in three dimensions in the Galactic Plane

We present three dimensional maps in monochromatic extinction $A_{\rm 0}$ and the extinction parameter $R_0$ within a few degrees of the Galactic plane. These are inferred using photometry from the Pan-STARRS1 and Spitzer Glimpse surveys of nearly $20$ million stars located in the region $l = 0-250^{\circ}$ and from $b = -4.5^{\circ}$ to $b=4.5^{\circ}$. Given the available stellar number density, we use an angular resolution of $7' \times 7'$ and steps of $1{\rm mag}$ in distance modulus. We simultaneously estimate distance modulus and effective temperature $T_{\rm eff}$ alongside the other parameters for stars individually using the method of \citet{Hanson2014} before combining these estimates to a complete map. The full maps are available via the MNRAS website.

astro-ph.GA↗

arXiv2016

The Pan-STARRS 1 Discoveries of five new Neptune Trojans

In this work we report the detection of seven Neptune Trojans (NTs) in the Pan-STARRS 1 (PS1) survey. Five of these are new discoveries, consisting of four L4 Trojans and one L5 Trojan. Our orbital simulations show that the L5 Trojan stably librates for only several million years. This suggests that the L5 Trojan must be of recent capture origin. On the other hand, all four new L4 Trojans stably occupy the 1:1 resonance with Neptune for more than 1 Gyr. They can, therefore, be of primordial origin. Our survey simulation results show that the inclination width of the Neptune Trojan population should be between $7^{\circ}$ and $27^{\circ}$ at $>$ 95% confidence, and most likely $\sim 11^{\circ}$. In this paper, we describe the PS1 survey, the Outer Solar System pipeline, the confirming observations, and the orbital/physical properties of the new Neptune Trojans.

astro-ph.EP↗