M. H. van Kerkwijk

Constraining the Spin-down of the Nearby Isolated Neutron Star RX J2143.0+0654 (2009)

The nearby isolated neutron stars are a group of seven relatively slowly rotating neutron stars that show thermal X-ray spectra, most with broad absorption features. They are interesting both because...

Deciphering the Pulsations of G 29-38 with Optical Time Series Spectroscopy (2008)

Magnetic field estimates for nearby isolated neutron stars (INS) help to constrain both the characteristics of the population and the nature of their peculiar X-ray spectra. From a series of...

Thompson, Susan E., Van Kerkwijk, M. H., Clemens, J. C.

We present optical time series spectroscopy of the pulsating white dwarf star G29-38 taken at the Very Large Telescope (VLT). By measuring the variations in brightness, Doppler shift, and line shape...

Timing the Nearby Isolated Neutron Star RX J1856.5-3754 (2007)

Van Kerkwijk, M. H., Kaplan, D. L.

RX J1856.5-3754 is the X-ray brightest among the nearby isolated neutron stars. Its X-ray spectrum is thermal, and is reproduced remarkably well by a black-body, but its interpretation has remained...

Determination of the mass of the neutron star in SMC X-1, LMC X-4 and Cen X-3 with VLT/UVES (2007)

Kaper, L., Van Kerkwijk, M. H., Heemskerk, M. H. M.

We present the results of a spectroscopic monitoring campaign of the OB-star companions to the eclipsing X-ray pulsars SMC X-1, LMC X-4 and Cen X-3. High-resolution optical spectra obtained with UVES...

The variable radio-to-X-ray spectrum of the magnetar XTE J1810-197 (2007)

Camilo, F., Ransom, S. M., Penalver, J., Karastergiou, A., Van Kerkwijk, M. H., Durant, M., ...

We have observed the 5.54s anomalous X-ray pulsar XTE J1810-197 at radio, millimeter, and infrared (IR) wavelengths, with the aim of learning about its broad-band spectrum. At the IRAM 30m telescope,...

VLBA measurement of the transverse velocity of the magnetar XTE J1810-197 (2007)

Helfand, D. J., Chatterjee, S., Brisken, W. F., Camilo, F., Reynolds, J., Van Kerkwijk, M. H., ...

We have obtained observations of the magnetar XTE J1810-197 with the Very Long Baseline Array at two epochs separated by 106 days, at wavelengths of 6 cm and 3.6 cm. Comparison of the positions...

The Distance to the Isolated Neutron Star RX J0720.4-3125 (2007)

Kaplan, D. L., Van Kerkwijk, M. H., Anderson, J.

We have used a set of dedicated astrometric data from the Hubble Space Telescope to measure the parallax and proper motion of the nearby neutron star RX J0720.4-3125. At each of eight epochs over two...

Isolated neutron stars: Magnetic fields, distances, and spectra (2006)

Van Kerkwijk, M. H., Kaplan, D. L.

We present timing measurements, astrometry, and high-resolution spectra of a number of nearby, thermally emitting, isolated neutron stars. We use these to infer magnetic field strengths and...

The masses of PSR J1911-5958A and its white dwarf companion (2006)

Bassa, C. G., Van Kerkwijk, M. H., Koester, D., Verbunt, F.

We present spectroscopic and photometric observations of the optical counterpart to PSR J1911-5958A, a millisecond pulsar located towards the globular cluster NGC 6752. We measure radial velocities...

Optical Detection of Two Intermediate Mass Binary Pulsar Companions (2006)

Jacoby, B. A., Chakrabarty, D., Van Kerkwijk, M. H., Kulkarni, S. R., Kaplan, D. L.

We report the detection of probable optical counterparts for two Intermediate Mass Binary Pulsar (IMBP) systems, PSR J1528-3146 and PSR J1757-5322. Recent radio pulsar surveys have uncovered a...

The ultra-cool white dwarf companion of PSR J0751+1807 (2006)

Bassa, C. G., Van Kerkwijk, M. H., Kulkarni, S. R.

We present optical and near-infrared observations with Keck of the binary millisecond pulsar PSR J0751+1807. We detect a faint, red object - with R=25.08+-0.07, B-R=2.5+-0.3, and R-I=0.90+-0.10 - at...

A Coherent Timing Solution for the Nearby Isolated Neutron Star RX J1308.6+2127/RBS 1223 (2005)

High-speed, multi-colour optical photometry of the anomalous X-ray pulsar 4U 0142+61 with ULTRACAM (2005)

We present a phase-connected timing solution for the nearby isolated neutron star RX J1308.6+2127 (RBS 1223). From dedicated Chandra observations as well as archival Chandra and XMM-Newton data...

Dhillon, V. S., Marsh, T. R., Hulleman, F., Van Kerkwijk, M. H., Shearer, A., Littlefair, S. P., ...

We present high-speed, multi-colour optical photometry of the anomalous X-ray pulsar 4U 0142+61, obtained with ULTRACAM on the 4.2-m William Herschel Telescope. We detect 4U 0142+61 at magnitudes of...

A Coherent Timing Solution for the Nearby Isolated Neutron Star RX J0720.4-3125 (2005)

Observations of the binary pulsar system PSR B1718-19 -- The Role of Tidal Circularisation (2005)

We present the results of a dedicated effort to measure the spin-down rate of the nearby isolated neutron star RX J0720.4-3125. Comparing arrival times of the 8.39-sec pulsations for data from...

Janssen, T., Van Kerkwijk, M. H.

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...

On the mass distribution of neutron stars in HMXBs (2005)

Kaper, L., Van Kerkwijk, M. H.

We present the results of a monitoring campaign of three eclipsing high-mass X-ray binaries (HMXBs: SMC X-1, LMC X-4 and Cen X-3). High-resolution VLT/UVES spectra are used to measure the radial...

Tam, C. R., Kaspi, V. M., Van Kerkwijk, M. H., Durant, M.

We present the results of a near-infrared monitoring program of the Anomalous X-ray Pulsar 1E 2259+586, performed at the Gemini Observatory. This program began three days after the pulsar's 2002 June...

Optical studies of companions to millisecond pulsars (2004)

Van Kerkwijk, M. H., Bassa, C. G., Jacoby, B. A., Jonker, P. G.

Optical observations of the companions of pulsars can help determine the properties of the binaries, as well as those of their components, and give clues to the preceding evolution. In this review,...

The Peculiar Pulsations of PY Vul (2004)

Thompson, Susan E., Clemens, J. C., Van Kerkwijk, M. H., O'Brien, M. Sean, Koester, D.

The pulsating white dwarf star PY Vul (G~185-32) exhibits pulsation modes with peculiar properties that set it apart from other variable stars in the ZZ Ceti (DAV) class. These peculiarities include...

Properties of neutron stars (2004)

A Strong, Broad Absorption Feature in the X-ray Spectrum of the Nearby Neutron Star RX J1605.3+3249 (2004)

I review attempts made to determine the properties of neutron stars. I focus on constraints on the maximum mass that a neutron star can have, and on attempts to measure neutron-star radii. So far,...

Van Kerkwijk, M. H., Kaplan, D. L., Durant, M., Kulkarni, S. R., Paerels, F.

We present X-ray spectra taken with XMM-Newton of RX J1605.3+3249, the third brightest in the class of nearby, thermally emitting neutron stars. In contrast to what is the case for the brightest...

A puzzling periodicity in the pulsating DA white dwarf G 117-B15A (2004)

Kotak, R., Van Kerkwijk, M. H., Clemens, J. C.

We present time-resolved optical spectrophotometry of the pulsatinghydrogen atmosphere (DA) white dwarf G 117-B15A. We find threeperiodicities in the pulsation spectrum (215 s, 272 s, and 304 s) all...

PSR J1909-3744, a Binary Millisecond Pulsar with a Very Small Duty Cycle (2003)

Jacoby, B. A., Bailes, M., Van Kerkwijk, M. H., Ord, S., Hotan, A., Kulkarni, S. R., ...

We report the discovery of PSR J1909-3744, a 2.95 millisecond pulsar in a nearly circular 1.53 day orbit. Its narrow pulse width of 43 microseconds allows pulse arrival times to be determined with...

X-ray Spectroscopy of Thermally Emitting Neutron Stars (2003)

Optical identification of the companion to PSR J1911-5958A, the pulsar binary in the outskirts of NGC 6752 (2003)

I describe recent high-resolution X-ray spectroscopy of surface emission from nearby, thermally emitting neutron stars. I focus on RX J0720.4-3125, RX J1308.6+2127, and RX J1605.3+3249, all of which...

Bassa, C. G., Verbunt, F., Van Kerkwijk, M. H., Homer, L.

We report on the identification of the optical counterpart of the binary millisecond pulsar PSR J1911-5958A, located in the outskirts of the globular cluster NGC 6752. At the position of the pulsar...

The radial velocity curve of HD153919 (4U1700-37) revisited (2003)

Hammerschlag-Hensberge, G., Van Kerkwijk, M. H., Kaper, L.

We have re-analysed all available high-resolution ultraviolet IUE spectra of the high-mass X-ray binary HD153919/4U1700-37. The radial velocity semi-amplitude of 20.6 +/- 1.0 km/s and orbital...

High Resolution Spectroscopy of the Pulsating White Dwarf G29-38 (2003)

Thompson, Susan E., Clemens, J. C., Van Kerkwijk, M. H., Koester, D.

We present the analysis of time-resolved, high resolution spectra of the cool white dwarf pulsator, G29-38. From measuring the Doppler shifts of the H-alpha core, we detect velocity changes as large...

Temperature and cooling age of the white dwarf companion of PSR J0218+4232 (2003)

Bassa, C. G., Van Kerkwijk, M. H., Kulkarni, S. R.

We report on Keck optical BVRI images and spectroscopy of the companion of the binary millisecond pulsar PSR J0218+4232. A faint bluish (V=24.2, B-V=0.25) counterpart is observed at the pulsar...

The Nearby Neutron Star RX J0720.4-3125 from Radio to X-rays (2003)

Kaplan, D. L., Van Kerkwijk, M. H., Marshall, H. L., Jacoby, B. A., Kulkarni, S. R., Frail, D. A.

We present radio, optical, ultraviolet, and X-ray observations of the isolated, thermally-emitting neutron star RX J0720.4-3125 using the Parkes radio telescope, the Very Large Array, the Hubble...

The Optical Counterpart of the Isolated Neutron Star RX J1605.3+3249 (2003)

Kaplan, D. L., Kulkarni, S. R., Van Kerkwijk, M. H.

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...

A new look at the pulsating DB white dwarf GD 358: Line-of-sight velocity measurements and constraints on model atmospheres (2003)

Kotak, R., Van Kerkwijk, M. H., Clemens, J. C., Koester, D.

We report on our findings of the bright, pulsating, helium atmospherewhite dwarf GD 358, based on time-resolved optical spectrophotometry. Weidentify 5 real pulsation modes and at least 6 combination...

A Probable Optical Counterpart for the Isolated Neutron Star RX J1308.6+2127 (2002)

Kaplan, D. K., Kulkarni, S. R., Van Kerkwijk, M. H.

Using a very deep observation with HST/STIS, we have searched for an optical counterpart to the nearby radio-quiet isolated neutron star RX J1308.6+2127 (RBS 1223). We have identified a single object...

X-ray Timing of the Enigmatic Neutron Star RX J0720.4-3125 (2002)

Kaplan, D. L., Kulkarni, S. R., Van Kerkwijk, M. H., Marshall, H. L.

RX J0720.4-3125 is the third brightest neutron star in the soft X-ray sky and has been a source of mystery since its discovery, as its long 8-s period separates it from the population of typical...

Time-resolved optical spectroscopy of the pulsating DA white dwarf HS 0507+0434B : New constraints on mode identification and pulsation properties (2002)

Kotak, Rubina, Van Kerkwijk, M. H., Clemens, J. C.

We present a detailed analysis of time-resolved optical spectra of the ZZ Ceti white dwarf, HS 0507+0434B. Using the wavelength dependence of observed mode amplitudes, we deduce the spherical degree,...

Pulsating or not? A search for hidden pulsations below the red edge of the ZZ Ceti instability strip (2002)

Kotak, R., Van Kerkwijk, M. H., Clemens, J. C., Bida, T. A.

The location of the red edge of the ZZ Ceti instability strip is definedobservationally as being the lowest temperature for which a white dwarfwith a H-rich atmosphere (DA) is known to exhibit...

A half-a-day long thermonuclear X-ray burst from KS 1731-260 (2001)

Kuulkers, E., Van Kerkwijk, M. H., Cornelisse, R., Smith, D. A., Heise, J., ...

We report on an approximately twelve hour long X-ray flare from the low-mass X-ray binary KS 1731-260. The flare has a rise time of less than 13 min and declines exponentially with a decay time of...

Identification of the optical and quiescent counterparts to the bright X-ray transient in NGC 6440 (2001)

Van Kerkwijk, M. H., Pooley, D., Verbunt, F., Wijnands, R., Lewin, W. H. G.

After 3 years of quiescence, the globular cluster NGC 6440 exhibited a bright transient X-ray source turning on in August 2001, as noted with the RXTE All-Sky Monitor. We carried out a short target...

The Parallax and Proper Motion of RX J1856.5-3754 Revisited (2001)

Kaplan, D. L., Van Kerkwijk, M. H., Anderson, J.

RX J1856.5-3754, a bright soft X-ray source believed to be the nearest thermally emitting neutron star, has commanded and continues to command intense interest from X-ray missions. One of the main...

Constraints on the equation of state of ultra-dense matter from observations of neutron stars (2001)

A possible faint near-infrared counterpart to the AXP 1E~2259+58.6 (2001)

I discuss constraints on the equation of state of matter at supra-nuclear densities that can be derived from observations of neutron stars. I focus on recent work on Vela X-1, which may well be...

Hulleman, F., Tennant, A. F., Van Kerkwijk, M. H., Kulkarni, S. R., Kouveliotou, C., Patel, S. K.

We present near-infrared and optical observations of the field of the Anomalous X-ray Pulsar 1E 2259+58.6 taken with the Keck telescope. We derive a subarcsecond Chandra position and tie it to our...

An unusual H-alpha nebula around RX J1856.5-3754 (2001)

The mass of the neutron star in Vela X-1 (2001)

We present spectroscopy and H alpha imaging of a faint nebula surrounding the X-ray bright, nearby neutron star RX J1856.5-3754. The nebula shows no strong lines other than the Hydrogen Balmer lines...

Barziv, O., Kaper, L., Van Kerkwijk, M. H., Telting, J. H., Van Paradijs, J.

We measured the radial-velocity curve of HD77581, the B-supergiant companion of the X-ray pulsar Vela X-1, using 183 high-resolution optical spectra obtained in a nine-month campaign. We derive...

Deep Radio, Optical, and Infrared Observations of SGR 1900+14 (2001)

Kaplan, D. L., Kulkarni, S. R., Frail, D. A., Van Kerkwijk, M. H.

We present HST/STIS, Keck J- and K_s-band, and VLA 332-MHz and 1400-MHz images of the region around the Soft Gamma-ray Repeater SGR 1900+14. No non-stellar sources were detected at the position of...

The IR counterpart of the black-hole candidate 4U 1630-47 (2001)

Augusteijn, T., Kuulkers, E., Van Kerkwijk, M. H.

We present K band photometry of the region including the radio error box of the soft X-ray transient 4U 1630-47 during its 1998 outburst. We detect a variable source at K=16.1 mag located inside the...

Optical spectroscopy and photometry of the isolated neutron star RX J1856.5-3754 (2001)

HST Observations of SGR 0526-66: New Constraints on Accretion and Magnetar Models (2001)

We present spectroscopy and imaging with the Very Large Telescope (VLT) of the neutron star RX J1856.5-2754. Little is known about the nature of this source other than that it is a nearby hot neutron...

Kaplan, D. L., Kulkarni, S. R., Van Kerkwijk, M. H., Rothschild, R. E., Lingenfelter, R. L., Marsden, D., ...

Soft Gamma-ray Repeaters (SGRs) are among the most enigmatic sources known today. Exhibiting huge X- and Gamma-ray bursts and flares, as well as soft quiescent X-ray emission, their energy source...

Mode Identification, Velocity Variations and the Red Edge of the ZZ Ceti Instability strip from time-resolved spectroscopy (2001)

Kotak, R., Van Kerkwijk, M. H.

Not Available

An Optical Counterpart to the Anomalous X-ray Pulsar 4U 0142+61 (2000)

Hulleman, F., Van Kerkwijk, M. H., Kulkarni, S. R.

The energy source of the anomalous X-ray pulsars is not well understood, hence their designation as anomalous. Unlike binary X-ray pulsars, no companions are seen, so the energy cannot be supplied by...

X-ray and optical follow-up observations of the August 1998 X-ray transient in NGC6440 (2000)

Verbunt, F., Van Kerkwijk, M. H., Heise, J.

The BeppoSAX Wide Field Cameras detected a transient in NGC6440 on 1998 Aug 22. ROSAT did not detect this source on 1998 Sep 8, indicating that the X-ray flux had decreased by a factor 400 at least,...

A deep search for the optical counterpart to the anomalous X-ray pulsar 1E 2259+58.6 (2000)

Hulleman, F., Van Kerkwijk, M. H., Verbunt, F. W. M., Kulkarni, S. R.

We present Keck R and I band images of the field of the anomalous X-ray pulsar 1E 2259+58.6. We derive an improved X-ray position from archival ROSAT HRI observations by correcting for systematic...

Neutron Star Mass Determinations (2000)

The Temperature and Cooling Age of the White-Dwarf Companion to the Millisecond Pulsar PSR B1855+09 (1999)

I review attempts made to determine the properties of neutron stars. The focus is on the maximum mass that a neutron star can have, or, conversely, the minimum mass required for the formation of a...

Van Kerkwijk, M. H., Bell, J. F., Kaspi, V. M., Kulkarni, S. R.

We report on Keck and {\em Hubble Space Telescope} observations of the binary millisecond pulsar PSR B1855+09. We detect its white-dwarf companion and measure $\mv=25.90\pm0.12$ and...

Surface motion in the pulsating DA white dwarf G 29-38 (1999)

Van Kerkwijk, M. H., Clemens, J. C., Wu, Y.

We present time-resolved spectrophotometry of the pulsating DA white dwarf G 29-38. As in previous broad-band photometry, the light curve shows the presence of a large number of periodicities. Many...

Mode identification from time-resolved spectroscopy of the pulsating white dwarf G 29-38 (1999)

Clemens, J. C., Van Kerkwijk, M. H., Wu, Y.

We have used time-resolved spectroscopy to measure the colour dependence of pulsation amplitudes in the DAV white dwarf G 29-38. Model atmospheres predict that mode amplitudes should change with...

Optical Observations of the Binary Pulsar System PSR B1718-19: Implications for Tidal Circularization (1999)

Van Kerkwijk, M. H., Kaspi, V. M., Klemola, A. R., Kulkarni, S. R., Lyne, A. G., Van Buren, D.

We report on Keck and Hubble Space Telescope optical observations of the eclipsing binary pulsar system PSR B1718-19, in the direction of the globular cluster NGC 6342. These reveal a faint star...

A new X-ray outburst in the globular cluster NGC 6440: SAX J1748.9-2021 (1999)

Verbunt, F., Strohmayer, T. E., Bazzano, A., Cocchi, M., Heise, J., ...

For the second time in 27 years a bright transient X-ray source has been detected coincident with the globular cluster NGC 6440. It was found to be active in August, 1998, with the Wide Field Camera...

A Massive White Dwarf Companion to the Eccentric Binary Pulsar System PSR B2303+46 (1999)

Optical Observations of the Isolated Neutron Star RX J0720.4-3125 (1998)

Pulsars in close, eccentric binary systems are usually assumed to have another neutron star as a companion. These double neutron star binaries have proven to be the best laboratories for experimental...

Kulkarni, S. R., Van Kerkwijk, M. H.

RX J0720.4-3125 is an unidentified bright soft X-ray source which shows pulsations at a 8.39 s period and has a thermal spectrum. We present deep B and R band images of its X-ray localization. We...

The Spectrum of the Brown Dwarf Gliese 229B (1998)

Oppenheimer, B. R., Kulkarni, S. R., Matthews, K., Van Kerkwijk, M. H.

We present a spectrum of the cool (T_eff = 900 K) brown dwarf Gliese 229B. This spectrum, with a relatively high signal-to-noise ratio per spectral resolution element (> 30), spans the wavelength...

Warped Disks as a Possible Origin of Torque Reversals in Accretion-Powered Pulsars (1998)

Van Kerkwijk, M. H., Chakrabarty, Deepto, Pringle, J. E.

Enigmatic transitions between spin-up and spin-down have been observed in several X-ray pulsars accreting matter via an accretion disk. In these transitions, the torque changes sign but remains at...

Unique White Dwarfs Accompanying Recycled Pulsars (1996)

The White Dwarf Companions of Recycled Pulsars (1996)

I introduce the two classes of pulsar, white-dwarf binaries, and describe for each what we have learned from a specific system, PSR J1012+5307 and PSR B0655+64, respectively, summarising what has...

The masses of the millisecond pulsar J1012+5307 and its white-dwarf companion (1996)

I review what properties of the white-dwarf companions of recycled pulsars can be inferred from optical observations, and discuss how these can help us understand the characteristics and evolution of...

Van Kerkwijk, M. H., Bergeron, P., Kulkarni, S. R.

We report on spectroscopy of the white-dwarf companion of the millisecond radio pulsar PSR J1012+5307. We find strong Balmer absorption lines, as would be expected for a cool DA white dwarf. The...

The Wolf-Rayet counterpart of Cygnus X-3 (1996)

Van Kerkwijk, M. H., Geballe, T. R., King, D. L., Van Paradijs, J.

We present orbital-phase resolved I and K-band spectroscopy of Cygnus X-3. All spectra show emission lines characteristic of Wolf-Rayet stars of the WN subclass. On time scales longer than about one...

Spectroscopy of the white-dwarf companions of PSR~0655+64 and 0820+02 (1995)