The Experts below are selected from a list of 107220 Experts worldwide ranked by ideXlab platform
Ann I Zabludoff - One of the best experts on this subject based on the ideXlab platform.
-
constraining very high mass population iii stars through he ii emission in galaxy bdf 521 at z 7 01
The Astrophysical Journal, 2015Co-Authors: Zheng Cai, Xiaohui Fan, Linhua Jiang, Romeel Dave, Yujin Yang, Ann I ZabludoffAbstract:Numerous theoretical models have long proposed that a strong He II λ1640 emission line is the most prominent and unique feature of massive Population III (Pop III) stars in high-redshift galaxies. The He II λ1640 line strength can constrain the mass and initial mass function (IMF) of Pop III stars. We use F132N narrowband filter on the Hubble Space Telescope's (HST) Wide Field Camera 3 to look for strong He II λ1640 emission in the galaxy BDF-521 at z = 7.01, one of the most distant spectroscopically confirmed galaxies to date. Using deep F132N narrowband imaging, together with our broadband imaging with F125W and F160W filters, we do not detect He II emission from this galaxy, but place a 2σ upper limit on the Flux of . This measurement corresponds to a 2σ upper limit on the Pop III star formation rate (SFRPopIII) of ~0.2 M ☉ yr–1, assuming a Salpeter IMF with 50 M/M ☉ 1000. From the high signal-to-noise broadband measurements in F125W and F160W, we fit the UV continuum for BDF-521. The Spectral Flux density is A–1, which corresponds to an overall unobscured SFR of ~5 M ☉ yr–1. Our upper limit on SFRPopIII suggests that massive Pop III stars represent 4% of the total star formation. Further, the HST high-resolution imaging suggests that BDF-521 is an extremely compact galaxy, with a half-light radius of 0.6 kpc.
-
constraining very high mass population iii stars through he ii emission in galaxy bdf 521 at z 7 01
arXiv: Astrophysics of Galaxies, 2014Co-Authors: Zheng Cai, Xiaohui Fan, Linhua Jiang, Romeel Dave, Yujin Yang, Ann I ZabludoffAbstract:Numerous theoretical models have long proposed that a strong He II 1640 emission line is the most prominent and unique feature of massive Population III (Pop III) stars in high redshift galaxies. The He II 1640 line strength can constrain the mass and IMF of Pop III stars. We use F132N narrowband filter on the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) to look for strong He II lambda 1640 emission in the galaxy BDF-521 at z=7.01, one of the most distant spectroscopically-confirmed galaxies to date. Using deep F132N narrowband imaging, together with our broadband imaging with F125W and F160W filters, we do not detect He II emission from this galaxy, but place a 2-sigma upper limit on the Flux of 5.3x10^-19 ergs s^-1 cm^-2. This measurement corresponds to a 2-sigma upper limit on the Pop III star formation rate (SFR_PopIII) of ~ 0.2 M_solar yr^-1, assuming a Salpeter IMF with 50< M/M_solar < 1000. From the high signal-to-noise broadband measurements in F125W and F160W, we fit the UV continuum for BDF-521. The Spectral Flux density is ~ 3.6x 10^-11 lambda^-2.32 ergs s^-1 cm^-2 A^-1, which corresponds to an overall unobscured SFR of ~ 5 M_solar yr^-1. Our upper limit on SFR_PopIII suggests that massive Pop III stars represent < 4% of the total star formation. Further, the HST high resolution imaging suggests that BDF-521 is an extremely compact galaxy, with a half-light radius of 0.6 kpc.
Romeel Dave - One of the best experts on this subject based on the ideXlab platform.
-
constraining very high mass population iii stars through he ii emission in galaxy bdf 521 at z 7 01
The Astrophysical Journal, 2015Co-Authors: Zheng Cai, Xiaohui Fan, Linhua Jiang, Romeel Dave, Yujin Yang, Ann I ZabludoffAbstract:Numerous theoretical models have long proposed that a strong He II λ1640 emission line is the most prominent and unique feature of massive Population III (Pop III) stars in high-redshift galaxies. The He II λ1640 line strength can constrain the mass and initial mass function (IMF) of Pop III stars. We use F132N narrowband filter on the Hubble Space Telescope's (HST) Wide Field Camera 3 to look for strong He II λ1640 emission in the galaxy BDF-521 at z = 7.01, one of the most distant spectroscopically confirmed galaxies to date. Using deep F132N narrowband imaging, together with our broadband imaging with F125W and F160W filters, we do not detect He II emission from this galaxy, but place a 2σ upper limit on the Flux of . This measurement corresponds to a 2σ upper limit on the Pop III star formation rate (SFRPopIII) of ~0.2 M ☉ yr–1, assuming a Salpeter IMF with 50 M/M ☉ 1000. From the high signal-to-noise broadband measurements in F125W and F160W, we fit the UV continuum for BDF-521. The Spectral Flux density is A–1, which corresponds to an overall unobscured SFR of ~5 M ☉ yr–1. Our upper limit on SFRPopIII suggests that massive Pop III stars represent 4% of the total star formation. Further, the HST high-resolution imaging suggests that BDF-521 is an extremely compact galaxy, with a half-light radius of 0.6 kpc.
-
constraining very high mass population iii stars through he ii emission in galaxy bdf 521 at z 7 01
arXiv: Astrophysics of Galaxies, 2014Co-Authors: Zheng Cai, Xiaohui Fan, Linhua Jiang, Romeel Dave, Yujin Yang, Ann I ZabludoffAbstract:Numerous theoretical models have long proposed that a strong He II 1640 emission line is the most prominent and unique feature of massive Population III (Pop III) stars in high redshift galaxies. The He II 1640 line strength can constrain the mass and IMF of Pop III stars. We use F132N narrowband filter on the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) to look for strong He II lambda 1640 emission in the galaxy BDF-521 at z=7.01, one of the most distant spectroscopically-confirmed galaxies to date. Using deep F132N narrowband imaging, together with our broadband imaging with F125W and F160W filters, we do not detect He II emission from this galaxy, but place a 2-sigma upper limit on the Flux of 5.3x10^-19 ergs s^-1 cm^-2. This measurement corresponds to a 2-sigma upper limit on the Pop III star formation rate (SFR_PopIII) of ~ 0.2 M_solar yr^-1, assuming a Salpeter IMF with 50< M/M_solar < 1000. From the high signal-to-noise broadband measurements in F125W and F160W, we fit the UV continuum for BDF-521. The Spectral Flux density is ~ 3.6x 10^-11 lambda^-2.32 ergs s^-1 cm^-2 A^-1, which corresponds to an overall unobscured SFR of ~ 5 M_solar yr^-1. Our upper limit on SFR_PopIII suggests that massive Pop III stars represent < 4% of the total star formation. Further, the HST high resolution imaging suggests that BDF-521 is an extremely compact galaxy, with a half-light radius of 0.6 kpc.
C Reyes - One of the best experts on this subject based on the ideXlab platform.
-
hubble space telescope detection of the millisecond pulsar j2124 3358 and its far ultraviolet bow shock nebula
The Astrophysical Journal, 2017Co-Authors: Blagoy Rangelov, G G Pavlov, Oleg Kargaltsev, Andreas Reisenegger, S Guillot, M H Van Kerkwijk, C ReyesAbstract:We observed the nearby millisecond pulsar J2124–3358 with the Hubble Space Telescope in broad far-UV (FUV) and optical filters. The pulsar is detected in both bands with Fluxes F(1250–2000 A) = (2.5 ± 0.3) × 10−16 erg s−1 cm−2 and F(3800–6000 A) = (6.4 ± 0.4) × 10−17 erg s−1 cm−2, which corresponds to luminosities of ≈5.8 × 1027 and 1.4 × 1027 erg s−1, for d = 410 pc and E(B − V) = 0.03. The optical-FUV spectrum can be described by a power-law model, , with slope α = 0.18–0.48 for a conservative range of color excess, E(B − V) = 0.01–0.08. Since a Spectral Flux rising with frequency is unusual for pulsar magnetospheric emission in this frequency range, it is possible that the spectrum is predominantly magnetospheric (power law with α < 0) in the optical, while it is dominated by thermal emission from the neutron star surface in the FUV. For a neutron star radius of 12 km, the surface temperature would be between 0.5 × 105 and 2.1 × 105 K for α ranging from −1 to 0, E(B − V) = 0.01–0.08, and d = 340–500 pc. In addition to the pulsar, the FUV images reveal extended emission that is spatially coincident with the known Hα bow shock, making PSR J2124–3358 the second pulsar (after PSR J0437−4715) with a bow shock detected in the FUV.
-
hubble space telescope detection of the millisecond pulsar j2124 3358 and its far ultraviolet bow shock nebula
arXiv: High Energy Astrophysical Phenomena, 2016Co-Authors: Blagoy Rangelov, G G Pavlov, Oleg Kargaltsev, Andreas Reisenegger, S Guillot, M H Van Kerkwijk, C ReyesAbstract:We observed a nearby millisecond pulsar J2124-3358 with the Hubble Space Telescope in broad far-UV (FUV) and optical filters. The pulsar is detected in both bands with Fluxes F(1250-2000 A)= (2.5+/-0.3)x10^-16 erg/s/cm^2 and F(3800-6000 A)=(6.4+/-0.4)x10^-17 erg/s/cm^2, which correspond to luminosities of ~5.8x10^27 and 1.4x10^27 erg/s, for d=410 pc and E(B-V)=0.03. The optical-FUV spectrum can be described by a power-law model, f_nu~nu^alpha, with slope alpha=0.18-0.48 for a conservative range of color excess, E(B-V)=0.01-0.08. Since a Spectral Flux rising with frequency is unusual for pulsar magnetospheric emission in this frequency range, it is possible that the spectrum is predominantly magnetospheric (power law with alpha<0) in the optical while it is dominated by thermal emission from the neutron star surface in the FUV. For a neutron star radius of 12 km, the surface temperature would be between 0.5x10^5 and 2.1x10^5 K, for alpha ranging from -1 to 0, E(B-V)=0.01-0.08, and d=340-500 pc. In addition to the pulsar, the FUV images reveal extended emission spatially coincident with the known Halpha bow shock, making PSR J2124-3358 the second pulsar (after PSR J0437-4715) with a bow shock detected in FUV.
F Pepe - One of the best experts on this subject based on the ideXlab platform.
-
a new infrared fabry perot based radial velocity reference module for the spirou radial velocity spectrograph
Astronomy and Astrophysics, 2017Co-Authors: Federica Cersullo, F Wildi, Bruno Chazelas, F PepeAbstract:Context. The field of exoplanet research is moving towards the detection and characterization of habitable planets. These exo-Earths can be easily found around low-mass stars by using either photometric transit or radial-velocity (RV) techniques. In the latter case the gain is twofold because the signal induced by the planet of a given mass is higher due to the more favourable planet-star mass ratio and because the habitable zone lies closer to the star. However, late-type stars emit mainly in the infrared (IR) wavelength range, which calls for IR instruments.Aims. SPIRou is a stable RV IR spectrograph addressing these ambitious scientific objectives. As with any other spectrograph, calibration and drift monitoring is fundamental to achieve high precision. However, the IR domain suffers from a lack of suitable reference Spectral sources. Our goal was to build, test and finally operate a Fabry-Perot-based RV-reference module able to provide the needed Spectral information over the full wavelength range of SPIRou.Methods. We adapted the existing HARPS Fabry-Perot calibrator for operation in the IR domain. After manufacturing and assembly, we characterized the FP RV-module in the laboratory before delivering it to the SPIRou integration site. In particular, we measured finesse, transmittance, and Spectral Flux of the system.Results. The measured finesse value of F = 12.8 corresponds perfectly to the theoretical value. The total transmittance at peak is of the order of 0.5%, mainly limited by fibre-connectors and interfaces. Nevertheless, the provided Flux is in line with the the requirements set by the SPIRou instrument. Although we could test the stability of the system, we estimated it by comparing the SPIRou Fabry-Perot with the already operating HARPS system and demonstrated a stability of better than 1 m s-1 during a night.Conclusions. Once installed on SPIRou, we will test the full Spectral characteristics and stability of the RV-reference module. The goal will be to prove that the line position and shape stability of all lines is better than 0.3 m s-1 between two calibration sequences (typically 24 h), such that the RV-reference module can be used to monitor instrumental drifts. In principle, the system is also intrinsically stable over longer time scales such that it can also be used for calibration purposes.
B J Butler - One of the best experts on this subject based on the ideXlab platform.
-
an accurate Flux density scale from 50 mhz to 50 ghz
Astrophysical Journal Supplement Series, 2017Co-Authors: R A Perley, B J ButlerAbstract:The Flux density scale of Perley and Butler (2013) is extended downwards to ~50 MHz by utilizing recent observations with the Karl G. Jansky Very Large Array (VLA) of 20 sources between 220 MHz and 48.1 GHz, and legacy VLA observations at 73.8 MHz. The derived Spectral Flux densities are placed on an absolute scale by utilizing the Baars et al. (1977) values of Cygnus A (3C405) for frequencies below 2 GHz, and the Mars-based polynomials for 3C286, 3C295, and 3C196 from Perley and Butler (2013) above 2 GHz. Polynomial expressions are presented for all 20 sources, with accuracy limited by the primary standards to 3 -- 5% over the entire frequency range. Corrections to the scales proposed by Perley and Butler (2013) and by Scaife and Heald (2012) are given.
-
an accurate Flux density scale from 1 to 50 ghz
Astrophysical Journal Supplement Series, 2013Co-Authors: R A Perley, B J ButlerAbstract:We develop an absolute Flux density scale for centimeter-wavelength astronomy by combining accurate Flux density ratios determined by the Very Large Array between the planet Mars and a set of potential calibrators with the Rudy thermophysical emission model of Mars, adjusted to the absolute scale established by the Wilkinson Microwave Anisotropy Probe. The radio sources 3C123, 3C196, 3C286, and 3C295 are found to be varying at a level of less than {approx}5% per century at all frequencies between 1 and 50 GHz, and hence are suitable as Flux density standards. We present polynomial expressions for their Spectral Flux densities, valid from 1 to 50 GHz, with absolute accuracy estimated at 1%-3% depending on frequency. Of the four sources, 3C286 is the most compact and has the flattest Spectral index, making it the most suitable object on which to establish the Spectral Flux density scale. The sources 3C48, 3C138, 3C147, NGC 7027, NGC 6542, and MWC 349 show significant variability on various timescales. Polynomial coefficients for the Spectral Flux density are developed for 3C48, 3C138, and 3C147 for each of the 17 observation dates, spanning 1983-2012. The planets Venus, Uranus, and Neptune are included in our observations, and we derive theirmore » brightness temperatures over the same frequency range.« less
-
an accurate Flux density scale from 1 to 50 ghz
arXiv: Instrumentation and Methods for Astrophysics, 2012Co-Authors: R A Perley, B J ButlerAbstract:We develop an absolute Flux density scale for cm-wavelength astronomy by combining accurate Flux density ratios determined by the VLA between the planet Mars and a set of potential calibrators with the Rudy thermophysical emission model of Mars, adjusted to the absolute scale established by WMAP. The radio sources 3C123, 3C196, 3C286 and 3C295 are found to be varying at a level of less than ~5% per century at all frequencies between 1 and 50 GHz, and hence are suitable as Flux density standards. We present polynomial expressions for their Spectral Flux densities, valid from 1 to 50 GHz, with absolute accuracy estimated at 1-3% depending on frequency. Of the four sources, 3C286 is the most compact and has the flattest Spectral index, making it the most suitable object on which to establish the Spectral Flux density scale. The sources 3C48, 3C138, 3C147, NGC7027, NGC6542, and MWC349 show significant variability on various timescales. Polynomial coefficients for the Spectral Flux density are developed for 3C48, 3C138, and 3C147 for each of the seventeen observation dates, spanning 1983 through 2012. The planets Venus, Uranus, and Neptune are included in our observations, and we derive their brightness temperatures over the same frequency range.