Showing papers by "R. P. Kudritzki published in 2018"

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

Abstract: Author(s): Scolnic, DM; Jones, DO; Rest, A; Pan, YC; Chornock, R; Foley, RJ; Huber, ME; Kessler, R; Narayan, G; Riess, AG; Rodney, S; Berger, E; Brout, DJ; Challis, PJ; Drout, M; Finkbeiner, D; Lunnan, R; Kirshner, RP; Sanders, NE; Schlafly, E; Smartt, S; Stubbs, CW; Tonry, J; Wood-Vasey, WM; Foley, M; Hand, J; Johnson, E; Burgett, WS; Chambers, KC; Draper, PW; Hodapp, KW; Kaiser, N; Kudritzki, RP; Magnier, EA; Metcalfe, N; Bresolin, F; Gall, E; Kotak, R; McCrum, M; Smith, KW | Abstract: 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 SNe Ia (0.03 l z l 0.68) with useful distance estimates of SNe Ia from the Sloan Digital Sky Survey (SDSS), SNLS, and various low-z and Hubble Space Telescope samples to form the largest combined sample of SNe Ia, consisting of a total of 1048 SNe Ia in the range of 0.01 l z l 2.3, which we call the Pantheon Sample. When combining Planck 2015 cosmic microwave background (CMB) measurements with the Pantheon SN sample, we find Wm = 0.307 ± 0.012 and w = -1.026 ± 0.041 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 ± 0.089 and wa = -0.222 ± 0.407 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× in the statistics of the PS1 sample, improved calibration and photometry, and stricter light-curve quality cuts. We find that 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 SNe Ia to measure dark energy.

A Luminous Transient Event in a Sample of WISE-selected Variable AGNs

Abstract: Recently Assef et al. presented two catalogs of active galactic nucleus (AGN) candidates over 30,093 deg(2) selected from the Wide-field Infrared Survey Explorer (WISE) observations. From their most reliable sample, Assef et al. identified 45 AGN candidates with the highest variability levels in the AllWISE catalog but that are not blazars. Here we present new spectroscopic observations of some of these targets to further constrain their nature. We also study their optical light curves using observations from the Catalina Real-Time Transient Survey (CRTS) and find that only seven show significant optical variability, and that five of those seven are spectroscopically classified as AGNs. In one of them, WISEA J094806.56+031801.7 (W0948+0318), we identify a transient event in the CRTS light curve. We present a detailed analysis of this transient and characterize it through its CRTS light curve and its multiwavelength spectral energy distribution obtained from GALEX, Pan-STARRS, and WISE observations. We find that the most likely source of the transient is a superluminous supernova (SLSN) in W0948+0318. We estimate the total radiated energy to be E = (1.6 +/- 0.3) x 10(52) erg, making it one of the most energetic SLSNe observed. Based on the lack of change in mid-IR color throughout and after the transient event, we speculate that the location of the SLSN is within the torus of the AGN. We identify nine possible analogs to W0948+0318 based on their WISE light curves. None show optically detected transients and hence suggest significant dust obscuration. Finally, we estimate a rate of >2 x 10(-7) yr(-1) per AGN for these transients under the conservative assumption that none of the identified analogs have a common origin with the transient in W0948+0318.

A Luminous Transient Event in a Sample of WISE-Selected Variable AGN.

Abstract: Recently Assef et al.(2018) presented two catalogs of AGN candidates over 30,093 deg^2 selected from the Wide-field Infrared Survey Explorer (WISE) observations. From their most reliable sample, Assef et al. (2018) identified 45 AGN candidates with the highest variability levels in the AllWISE catalog, but that are not blazars. Here we present new spectroscopic observations of some of these targets to further constrain their nature. We also study their optical lightcurves using observations from CRTS, and find that only seven show significant optical variability, and that five of those seven are spectroscopically classified as AGN. In one of them, WISEA J094806.56+031801.7 (W0948+0318), we identify a transient event in the CRTS lightcurve. We present a detailed analysis of this transient, and characterize it through its CRTS lightcurve and its multi-wavelength spectral energy distribution obtained from GALEX, Pan-STARRS and WISE observations. We find that the most likely source of the transient is a super-luminous supernova (SLSN) in W0948+0318. We estimate the total radiated energy to be E=1.6\pm 0.3 x 10^52 erg, making it one of the most energetic SLSN observed. Based on the lack of change in mid-IR color throughout and after the transient event, we speculate that the location of the SLSN is within the torus of the AGN. We identify 9 possible analogs to W0948+0318 based on their WISE lightcurves. None show optically detected transients and hence suggest significant dust obscuration. Finally, we estimate a rate of >2x10^-7 yr^-1 per AGN for these transients under the conservative assumption that none of the identified analogs have a common origin with the transient in W0948+0318.

On a new and homogeneous metallicity scale for Galactic classical Cepheids - I. Physical parameters

Abstract: We gathered more than 1130 high-resolution optical spectra for more than 250 Galactic classical Cepheids. The spectra were collected with different optical spectrographs: UVES at VLT, HARPS at 3.6m, FEROS at 2.2m MPG/ESO, and STELLA. To improve the effective temperature estimates, we present more than 150 new line depth ratio (LDR) calibrations that together with similar calibrations already available in the literature allowed us to cover a broad range in wavelength (between 5348 and 8427 angstrom) and in effective temperatures (between 3500 and 7700 K). This means the unique opportunity to cover both the hottest and coolest phases along the Cepheid pulsation cycle and to limit the intrinsic error on individual measurements at the level of ~100 K. Thanks to the high signal-to-noise ratio of individual spectra we identified and measured hundreds of neutral and ionized lines of heavy elements, and in turn, have the opportunity to trace the variation of both surface gravity and microturbulent velocity along the pulsation cycle. The accuracy of the physical parameters and the number of Fe I (more than one hundred) and Fe II (more than ten) lines measured allowed us to estimate mean iron abundances with a precision better than 0.1 dex. Here we focus on 14 calibrating Cepheids for which the current spectra cover either the entire or a significant portion of the pulsation cycle. The current estimates of the variation of the physical parameters along the pulsation cycle and of the iron abundances agree quite well with similar estimates available in the literature. Independent homogeneous estimates of both physical parameters and metal abundances based on different approaches that can constrain possible systematics are highly encouraged.

A new and homogeneous metallicity scale for Galactic classical Cepheids - I. Physical parameters

Abstract: We gathered more than 1130 high-resolution optical spectra for more than 250 Galactic classical Cepheids. The spectra were collected with the optical spectrographs UVES at VLT, HARPS at 3.6 m, FEROS at 2.2 m MPG/ESO, and STELLA. To improve the effective temperature estimates, we present more than 150 new line depth ratio (LDR) calibrations that together with similar calibrations already available in the literature allowed us to cover a broad range in wavelength (5348 ≤ λ ≤ 8427 A) and in effective temperature (3500 ≤ T eff ≤ 7700 K). This gives us the unique opportunity to cover both the hottest and coolest phases along the Cepheid pulsation cycle and to limit the intrinsic error on individual measurements at the level of ~100 K. As a consequence of the high signal-to-noise ratio of individual spectra, we identified and measured hundreds of neutral and ionized lines of heavy elements, and in turn, have the opportunity to trace the variation of both surface gravity and microturbulent velocity along the pulsation cycle. The accuracy of the physical parameters and the number of Fe I (more than one hundred) and Fe II (more than ten) lines measured allowed us to estimate mean iron abundances with a precision better than 0.1 dex. We focus on 14 calibrating Cepheids for which the current spectra cover either the entire or a significant portion of the pulsation cycle. The current estimates of the variation of the physical parameters along the pulsation cycle and of the iron abundances agree very well with similar estimates available in the literature. Independent homogeneous estimates of both physical parameters and metal abundances based on different approaches that can constrain possible systematics are highly encouraged.

On the chemical abundances of Miras in clusters: V1 in the metal-rich globular NGC 5927

Abstract: We present the first spectroscopic abundance determination of iron, alpha-elements (Si, Ca and Ti) and sodium for the Mira variable V1 in the metal-rich globular cluster NGC 5927. We use high-resolution (R~ 28,000), high signal-to-noise ratio (~200) spectra collected with WINERED, a near-infrared (NIR) spectrograph covering simultaneously the wavelength range 0.91--1.35 micron. The effective temperature and the surface gravity at the pulsation phase of the spectroscopic observation were estimated using both optical (V) and NIR time-series photometric data. We found that the Mira is metal-rich ([Fe/H]=-0.55 \pm 0.15) and moderately alpha-enhanced ([alpha/Fe]=0.15 \pm 0.01, sigma=0.2). These values agree quite well with the mean cluster abundances based on high-resolution optical spectra of several cluster red giants available in the literature ([Fe/H]=-0.47 \pm 0.06, [alpha/Fe]=+0.24 \pm 0.05). We also found a Na abundance of +0.35 \pm 0.20 that is higher than the mean cluster abundance based on optical spectra (+0.18 \pm 0.13). However, the lack of similar spectra for cluster red giants and that of corrections for departures from local-thermodynamical equilibrium prevents us from establishing whether the difference is intrinsic or connected with multiple populations. These findings indicate a strong similarity between optical and NIR metallicity scales in spite of the difference in the experimental equipment, data analysis and in the adopted spectroscopic diagnostics.

On the Chemical Abundances of Miras in Clusters: V1 in the Metal-rich Globular NGC 5927

Abstract: We present the first spectroscopic abundance determination of iron, a-elements (Si, Ca, and Ti), and sodium for the Mira variable V1 in the metal-rich globular cluster NGC. 5927. We use high-resolution (R similar to 28,000), high signal-to-noise ratio (similar to 200) spectra collected with WINERED, a near-infrared (NIR) spectrograph covering simultaneously the wavelength range 0.91-1.35 mu m. The effective temperature and the surface gravity at the pulsation phase of the spectroscopic observation were estimated using both optical (V) and NIR time-series photometric data. We found that the Mira is metal-rich ([Fe/H] = -0.55 +/- 0.15) and moderately a-enhanced ([alpha/Fe] = 0.15 +/- 0.01, sigma = 0.2). These values agree quite well with the mean cluster abundances based on high-resolution optical spectra of several cluster red giants available in the literature ([Fe/H] = -0.47 +/- 0.06, [alpha/Fe] = +0.24 +/- 0.05). We also found a Na abundance of +0.35 +/- 0.20 that is higher than the mean cluster abundance based on optical spectra (+0.18 +/- 0.13). However, the lack of similar spectra for cluster red giants and that of corrections for departures from local thermodynamical equilibrium prevents us from establishing whether the difference is intrinsic or connected with multiple populations. These findings indicate a strong similarity between optical and NIR metallicity scales in spite of the difference in the experimental equipment, data analysis, and in the adopted spectroscopic diagnostics.

Charge diffusion variations in Pan-STARRS1 CCDs.

Abstract: 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-STARRS 1 Gigapixel Camera. We have identified systematic spatial variations in the photometric measurements and stellar profiles that 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 that 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.

Supergiant Stars as Abundance Probes

Abstract: Abstract By compiling abundances from red and blue supergiants (SGs) within the Local Universe, I present the Mass-Metallicity relation (MZR) using stellar tracers, demonstrating the excellent internal consistency. Comparing this result with nebular tracers, those empirically calibrated to direct-method studies provide the most consistent results.