Book Reviews

Reviews of the following books: Landscape with Figures: Nature & Culture in New England by Kent C. Ryden; Imagining New England: Explorations of Regional Identity from the Pilgrims to the Mid-Twentieth Century by Joseph A. Conforti. A Good and Wise Measure: the Search for the American-Canadian Boundary, 1783-1842 by Francis M. Carroll. John Ford in Focus: Essays on the Filmmaker’s Life and Work, edited by Kevin L. Stoehr and Michael C. Connolly. Styles Bridges: Yankee Senator by James J. Kiepper. Giving Voters a Voice: The Origins of the Initiative and Referendum in America by Steven L. Piott. Androscoggin County, Maine – 150th: A Pictorial Sesquicentennial History, 1854 – 2004 edited by Michael C. Lord and W. Dennis Stires. Down on the Island, Up on the Main: A Recollected History of South Bristol, Maine compiled and annotated by Ellen Vincen

T Pyxidis: The First Cataclysmic Variable with a Collimated Jet

We present the first observational evidence for a collimated jet in a cataclysmic variable system; the recurrent nova T Pyxidis. Optical spectra show bipolar components of H$\alpha$ with velocities $\sim 1400 km/s$, very similar to those observed in the supersoft X-ray sources and in SS 433. We argue that a key ingredient of the formation of jets in the supersoft X-ray sources and T Pyx (in addition to an accretion disk threaded by a vertical magnetic field), is the presence of nuclear burning on the surface of the white dwarf.Comment: 10 pages 2 figures to appear in ApJ Letter

The massive neutron star or low-mass black hole in 2S0921-630

We report on optical spectroscopy of the eclipsing Halo LMXB 2S0921-630, that reveals the absorption line radial velocity curve of the K0III secondary star with a semi-amplitude K_2=92.89 +/- 3.84 km/s, a systemic velocity $\gamma$=34.9 +/- 3.3 \kms and an orbital period P_orb of 9.0035 +/- 0.0029 day (1-sigma). Given the quality of the data, we find no evidence for the effects of X-ray irradiation. Using the previously determined rotational broadening of the mass donor, and applying conservative limits on the orbital inclination, we constrain the compact object mass to be 2.0-4.3 Msolar (1-sigma), ruling out a canonical neutron star at the 99% level. Since the nature of the compact object is unclear, this mass range implies that the compact object is either a low-mass black hole with a mass slightly higher than the maximum neutron star mass (2.9 Msolar) or a massive neutron star. If the compact object is a black hole, it confirms the prediction of the existence of low-mass black holes, while if the object is a massive neutron star its high mass severely constrains the equation of state of nuclear matter.Comment: Accepted by ApJ

A new mass-ratio for the X-ray Binary X2127+119 in M15?

The luminous low-mass X-ray binary X2127+119 in the core of the globular cluster M15 (NGC 7078), which has an orbital period of 17 hours, has long been assumed to contain a donor star evolving off the main sequence, with a mass of 0.8 solar masses (the main-sequence turn-off mass for M15). We present orbital-phase-resolved spectroscopy of X2127+119 in the H-alpha and He I 6678 spectral region, obtained with the Hubble Space Telescope. We show that these data are incompatible with the assumed masses of X2127+119's component stars. The continuum eclipse is too shallow, indicating that much of the accretion disc remains visible during eclipse, and therefore that the size of the donor star relative to the disc is much smaller in this high-inclination system than the assumed mass-ratio allows. Furthermore, the flux of X2127+119's He I 6678 emission, which has a velocity that implies an association with the stream-disc impact region, remains unchanged through eclipse, implying that material from the impact region is always visible. This should not be possible if the previously-assumed mass ratio is correct. In addition, we do not detect any spectral features from the donor star, which is unexpected for a 0.8 solar-mass sub-giant in a system with a 17-hour period.Comment: 6 pages, 4 figures, accepted by A&

Doppler tomography of the transient X-ray binary Centaurus X-4 in quiescence

We present ESO-NTT low resolution spectroscopy of the neutron star X-ray transient Cen X-4 in quiescence over a complete orbital cycle. Our data reveal the presence of a K3-7 V companion which contributes 63% to the 5600-6900A flux and orbits the neutron star with a velocity semi-amplitude of K_2=145.8 +/- 1.0 km s^{-1}. This, combined with a previous determination of the inclination angle and mass ratio, yields a neutron star and companion mass of M_1=1.5 +/- 1.0 M_Sun and M_2=0.31 +/- 0.27 M_Sun, respectively. The mass donor is thus undermassive for the inferred spectral type indicating it is probably evolved, in agreement with previous studies. Doppler tomography of the H_alpha line shows prominent emission located on the companion and a slightly asymmetric accretion disc distribution similar to that seen in systems with precessing eccentric discs. Strong H_alpha emission from the companion can be explained by X-ray irradiation from the primary. No evidence is found for a hot spot in H_alpha, whereas one is revealed via Doppler tomography of the HeI lines. This can be interpreted as the hot spot and outer regions of the disc being at a higher temperature than in other systems.Comment: 9 pages, 5 figures, accepted for publication in A&

The mass of the neutron star in Cyg X-2 (V1341 Cyg)

Cygnus X-2 is one of the brightest and longest known X-ray sources. We present high resolution optical spectroscopy of Cyg X-2 obtained over 4 years which gives an improved mass function of 0.69 +/- 0.03 Msun (1 sigma error). In addition, we resolve the rotationally broadened absorption features of the secondary star for the first time, deriving a rotation speed of vsin(i) = 34.2 +/- 2.5 km per s (1 sigma error) which leads to a mass ratio of q = M_c/M_x = 0.34 +/- 0.04 (1 sigma error), assuming a tidally-locked and Roche lobe-filling secondary). Hence with the lack of X-ray eclipses (i.e. i <~ 73 degrees) we can set firm 95% confidence lower limits to the neutron star mass of M_x > 1.27 Msun and to the companion star mass of M_c > 0.39 Msun. However, by additionally requiring that the companion must exceed 0.75 Msun (as required theoretically to produce a steady low-mass X-ray binary), then M_x > 1.88 Msun and i < 61 degrees (95% confidence lower and upper limit, respectively), thereby making Cyg X-2 the highest mass neutron star measured to date. If confirmed this would set significant constraints on the equation of state of nuclear matter.Comment: 16 pages, 4 figures, ApJ Letters, accepted, LaTeX, aasms4.st

Correlated X-ray and Optical Variability in V404 Cyg in Quiescence

We report simultaneous X-ray and optical observations of V404 Cyg in quiescence. The X-ray flux varied dramatically by a factor of >20 during a 60ks observation. X-ray variations were well correlated with those in Halpha, although the latter include an approximately constant component as well. Correlations can also be seen with the optical continuum, although these are less clear. We see no large lag between X-ray and optical line variations; this implies they are causally connected on short timescales. As in previous observations, Halpha flares exhibit a double-peaked profile suggesting emission distributed across the accretion disk. The peak separation is consistent with material extending outwards to at least the circularization radius. The prompt response in the entire Halpha line confirms that the variability is powered by X-ray (and/or EUV) irradiation.Comment: 5 pages; Accepted for publication in the Astrophysical Journal Letter

A Concept for an STJ-based Spectrograph

We describe a multi-order spectrograph concept suitable for 8m-class telescopes, using the intrinsic spectral resolution of Superconducting Tunneling Junction detectors to sort the spectral orders. The spectrograph works at low orders, 1-5 or 1-6, and provides spectral coverage with a resolving power of R~8000 from the atmospheric cutoff at 320 nm to the long wavelength end of the infrared H or K band at 1800 nm or 2400 nm. We calculate that the spectrograph would provide substantial throughput and wavelength coverage, together with high time resolution and sufficient dynamic range. The concept uses currently available technology, or technologies with short development horizons, restricting the spatial sampling to two linear arrays; however an upgrade path to provide more spatial sampling is identified. All of the other challenging aspects of the concept - the cryogenics, thermal baffling and magnetic field biasing - are identified as being feasible.Comment: Accepted in Monthly Notices of the Royal Astronomical Society, 12 pages with 10 figure

On the triple nature of the X-ray source 4U2129+47 (= V1727 Cyg)

Context. In quiescence, the proposed optical counterpart to the neutron star low mass X-ray binary 4U 2129+47 (V1727 Cyg) shows a spectrum consistent with a late F-type subgiant and no radial velocity variations on the 5.24 hour binary period. This could imply that V1727 Cyg is a chance line of sight interloper. Radial velocity measurements, however, showed evidence for a longer term ~40 km/s shift, which suggested that 4U 2129+47 could be a hierarchical triple system, with the F-type star in a wide orbit about the inner low mass X-ray binary. Aims. In order to confirm the long-term radial velocity shift reported in Garcia et al. (1989) and its amplitude, we obtained spectroscopic observations of V1727 Cyg during 1996 and 1998 with the William Herschel Telescope using the ISIS spectrograph. Methods. We determined radial velocities from the ISIS spectra by means of the cross-correlation technique with a template spectrum. Results. The resulting radial velocities show variations with a maximum amplitude of ~40 km/s, confirming previous results and supporting the F-type star as being the third body in a hierarchical triple system. The odds that this star could be an interloper are ~3e-6Comment: 3 Pages, 2 Figures. Revised version in form accepted for publication in A&

Irradiation of the secondary star in X-ray Nova Scorpii 1994 (=GRO J1655--40)

We have obtained intermediate resolution optical spectra of the black-hole candidate Nova Sco 1994 in June 1996, when the source was in an X-ray/optical active state (R~15.05). We measure the radial velocity curve of the secondary star and obtain a semi-amplitude of 279+/-10 km/s; a value which is 30 per cent larger than the value obtained when the source is in quiescence. Our large value for K_2 is consistent with 60 +9,-7 per cent of the secondary star's surface being heated; compared to 35 per cent, which is what one would expect if only the inner face of the secondary star were irradiated. Effects such as irradiation-induced flows on the secondary star may be important in explaining the observed large value for K_2.Comment: 5 pages, 2 figures, accepted by MNRA