M. H. van Kerkwijk

University of Toronto

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S. R. Kulkarni

California Institute of Technology

D. L. Kaplan

University of Wisconsin–Milwaukee

Ue‐Li Pen

Canadian Institute for Theoretical Astrophysics

Ray Jayawardhana

Cornell University

R. P. Breton

University of Manchester

Robert Main

McGill University

A. Brandeker

AlbaNova

J. C. Clemens

University of North Carolina at Chapel Hill

L. Kaper

University of Amsterdam

V. M. Kaspi

McGill University

Cooperative Institutions

Max Planck Society

118

California Institute of Technology

101

Centre National de la Recherche Scientifique

University of Toronto

Max Planck Institute for Radio Astronomy

University of Sydney

Commonwealth Scientific and Industrial Research Organisation

Center for Astrophysics Harvard & Smithsonian

Space Telescope Science Institute

Australian National University

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Array programming with NumPy

Nature (2020)

C. R. Harris K. Jarrod Millman Stéfan van der Walt Ralf Gommers Pauli Virtanen

Abstract Array programming provides a powerful, compact and expressive syntax for accessing, manipulating and operating on data in vectors, matrices and higher-dimensional arrays. NumPy is the primary array programming library for the Python language. It has an essential role in research analysis pipelines in fields as diverse as physics, chemistry, astronomy, geoscience, biology, psychology, materials science, engineering, finance and economics. For example, in astronomy, NumPy was an important part of the software stack used in the discovery of gravitational waves 1 and in the first imaging of a black hole 2 . Here we review how a few fundamental array concepts lead to a simple and powerful programming paradigm for organizing, exploring and analysing scientific data. NumPy is the foundation upon which the scientific Python ecosystem is constructed. It is so pervasive that several projects, targeting audiences with specialized needs, have developed their own NumPy-like interfaces and array objects. Owing to its central position in the ecosystem, NumPy increasingly acts as an interoperability layer between such array computation libraries and, together with its application programming interface (API), provides a flexible framework to support the next decade of scientific and industrial analysis.

10.1038/s41586-020-2649-2

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Citations (16,307)

Observations of the companion to the pulsar PSR B1718-19 - The role of tidal circularisation

Astronomy and Astrophysics (2005)

Tim Janssen M. H. van Kerkwijk

We present optical and infrared observations taken with the Very Large Telescope of the eclipsing binary pulsar system PSR B1718-19. The candidate companion of the pulsar, identified earlier in Hubble Space Telescope observations, has been detected in all three bands, R , I , and J . These detections allowed us to derive constraints on temperature, radius, and mass, pointing to a companion that has expanded to a radius between one of a main sequence star and one at the Roche-limit. We focus on the role of tidal circularisation in the system, which will have transformed the initially eccentric orbit expected from formation scenarios into the nearly circular orbit presently observed. Based on simple energy balance arguments, we are able to draw a picture of the companion's evolution resulting from the energy deposition in the star due to circularisation. In this picture, our measurement of the companion's parameters is consistent with the expected initial eccentricity. However, with the present understanding of tidal dissipation, it remains difficult to account for the short time in which the system was circularised.

Orbit (dynamics)

Eccentricity (behavior)

Roche limit

Roche lobe

Spitzer Space Telescope

Circular orbit

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Citations (7)

The X‐Ray Position and Optical Counterpart of the Accretion‐powered Millisecond Pulsar XTE J1814−338

The Astrophysical Journal (2005)

Miriam I. Krauss Zhongxiang Wang A. Dullighan Adrienne M. Juett D. L. Kaplan

We report the precise optical and X-ray localization of the 3.2 ms accretion-powered X-ray pulsar XTE J1814-338 with data from the Chandra X-Ray Observatory as well as optical observations conducted during the 2003 June discovery outburst. Optical imaging of the field during the outburst of this soft X-ray transient reveals an R = 18 star at the X-ray position. This star is absent (R > 20) from an archival 1989 image of the field and brightened during the 2003 outburst, and we therefore identify it as the optical counterpart of XTE J1814-338. The best source position derived from optical astrometry is R.A. = 18h13m39.s04, Dec.= -33d46m22.3s (J2000). The featureless X-ray spectrum of the pulsar in outburst is best fit by an absorbed power-law (with photon index = 1.41 +- 0.06) plus blackbody (with kT = 0.95 +- 0.13 keV) model, where the blackbody component contributes approximately 10% of the source flux. The optical broad-band spectrum shows evidence for an excess of infrared emission with respect to an X-ray heated accretion disk model, suggesting a significant contribution from the secondary or from a synchrotron-emitting region. A follow-up observation performed when XTE J1814-338 was in quiescence reveals no counterpart to a limiting magnitude of R = 23.3. This suggests that the secondary is an M3 V or later-type star, and therefore very unlikely to be responsible for the soft excess, making synchroton emission a more reasonable candidate.

Black-body radiation

X-ray pulsar

10.1086/430595

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Citations (38)

Ultra-soft sources as supernova type Ia progenitors

arXiv (Cornell University) (2011)

Kelly Lepo M. H. van Kerkwijk

Missing from the usual considerations of nuclear burning white dwarfs as Type Ia supernova progenitors are systems with very higher mass transfer rates, where more material than is needed for steady burning accretes on the white dwarf. This will move out the photosphere of the white dwarf, causing it to emit at longer wavelengths. Thus, we propose the name ultra-soft source (USS) for these objects. We present a VLT/FLAMES survey looking for USS in the SMC, selected to be bright in the far UV and with blue far UV-V colors. While we find some unusual objects, and recover known planetary nebula and WR stars, we detect no objects with strong He II lines, which should be a signature of USS. This null result either puts an upper limit on the number of USS in the SMC, or shows that we do not understand what the optical spectra of such objects will look like. We also discuss the unusual LMC [WN] planetary nebula LMC N66 as a possible example of an USS. It has a luminosity consistent with that expected, and its spectra show incompletely CNO-processed material - strong helium lines, some hydrogen, enhanced nitrogen and depleted carbon. It also shows periodic outbursts. USS may resemble N66 in quiescence. However, it lacks a FUV excess, contrary to our predictions.

10.48550/arxiv.1109.4394

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Citations (1)

A puzzling periodicity in the pulsating DA white dwarf G 117-B15A

Carolina Digital Repository (University of North Carolina at Chapel Hill) (2004)

R. Kotak M. H. van Kerkwijk J. C. Clemens

White (mutation)

10.17615/t54y-2d42

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The Optical Counterpart of the Isolated Neutron Star RX J1605.3+3249

The Astrophysical Journal (2003)

D. L. Kaplan S. R. Kulkarni M. H. van Kerkwijk

We have detected the optical counterpart to the nearby isolated neutron star RX J1605.3+3249 using observations from the Space Telescope Imaging Spectrometer aboard the Hubble Space Telescope. The counterpart, with m50CCD = 26.84 ± 0.07 mag and very blue colors, lies close to the ROSAT HRI error circle and within the Chandra error circle. The spectrum is consistent with a Rayleigh-Jeans tail whose emission is a factor of ≈14 above the extrapolation of the X-ray blackbody, and the source has an unabsorbed X-ray-to-optical flux ratio of log(fX/fopt) = 4.4, similar to that of other isolated neutron stars. This confirms the classification of RX J1605.3+3249 as a neutron star.

ROSAT

Black-body radiation

Star (game theory)

10.1086/375523

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Citations (42)

A new look at the pulsating DB white dwarf GD 358: Line-of-sight velocity measurements and constraints on model atmospheres

Carolina Digital Repository (University of North Carolina at Chapel Hill) (2003)

R. Kotak M. H. van Kerkwijk J. C. Clements D. Koester

Line (geometry)

Line-of-sight

White (mutation)

Sight

10.17615/qhbg-hr11

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Citations (0)

Cygnus X-3 an evolutionary missing link found?

Symposium - International Astronomical Union (1995)

M. H. van Kerkwijk

I review the properties of the X-ray source Cygnus X-3, and the evidence that is available that indicates that its companion is a Wolf-Rayet star. I focus on the interpretation of spectra of its infrared counterpart. Considering all data, I conclude that the companion is indeed a WR star, and I discuss the ramifications of this conclusion for our understanding of WR stars in general.

Wolf–Rayet star

Star (game theory)

Link (geometry)

10.1017/s0074180900202635

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An optical counterpart to the anomalous X-ray pulsar 4U0142+61

Nature (2000)

F. Hulleman M. H. van Kerkwijk S. R. Kulkarni

Magnetar

Rotational energy

X-ray pulsar

High-energy astronomy

10.1038/35047024

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Citations (128)

Spectroscopy of HD 77581 and the mass of Vela X-1

arXiv (Cornell University) (1995)

M. H. van Kerkwijk J.A. van Paradijs E. J. Zuiderwijk G. Hammerschlag–Hensberge L. Kaper

We present new high-resolution, high signal-to-noise optical spectra of HD 77581, the optical counterpart of the X-ray source Vela X-1, and determine radial velocities from these spectra, as well as from high-resolution IUE spectra and from digitized photographic spectra. The measured velocities show strong deviations from a pure Keplerian radial-velocity curve, which are autocorrelated within one night, but not from one night to another. Since lines of different ions exhibit very similar changes in profile, these deviations most likely reflect largescale motions of the stellar surface akin to non-radial pulsations. A possible cause could be that the varying tidal force exerted by the neutron star in its eccentric orbit excites high-order pulsation modes in the optical star which interfere constructively for short time intervals. The effect of such velocity excursions on the orbital solution is estimated by means of a Monte-Carlo simulation technique. We investigate sources of systematic error, due to, e.g., the tidal deformation of the star, and find, in particular, evidence for a systematic perturbation of the radial velocity near the time of velocity minimum. This possible distortion severely compromises the accuracy of the radial-velocity amplitude, leading to a 95% confidence range of 18.0-28.2kms(-1) The corresponding 95% confidence limits of the masses are given by M(x) = 1.9(-0.5)(+0.7) M. and M(opt) = 23.5(-1.5)(+2.2) M..

Radial velocity

Vela

Circular orbit

Orbital speed

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Citations (9)