4 research outputs found
The second data release of the INT Photometric Ha Survey of the Northern Galactic Plane (IPHAS DR2)
The INT/WFC Photometric Hα Survey of the Northern Galactic Plane (IPHAS) is a 1800 deg2 imaging survey covering Galactic latitudes |b| < 5° and longitudes ℓ = 30°–215° in the r, i, and Hα filters using the Wide Field Camera (WFC) on the 2.5-m Isaac Newton Telescope (INT) in La Palma. We present the first quality-controlled and globally calibrated source catalogue derived from the survey, providing single-epoch photometry for 219 million unique sources across 92 per cent of the footprint. The observations were carried out between 2003 and 2012 at a median seeing of 1.1 arcsec (sampled at 0.33 arcsec pixel−1) and to a mean 5σ depth of 21.2 (r), 20.0 (i), and 20.3 (Hα) in the Vega magnitude system. We explain the data reduction and quality control procedures, describe and test the global re-calibration, and detail the construction of the new catalogue. We show that the new calibration is accurate to 0.03 mag (root mean square) and recommend a series of quality criteria to select accurate data from the catalogue. Finally, we demonstrate the ability of the catalogue's unique (r − Hα, r − i) diagram to (i) characterize stellar populations and extinction regimes towards different Galactic sightlines and (ii) select and quantify Hα emission-line objects. IPHAS is the first survey to offer comprehensive CCD photometry of point sources across the Galactic plane at visible wavelengths, providing the much-needed counterpart to recent infrared surveys
Multi-wavelength observations of the EUV variable metal-rich white dwarf GD 394
We present new Hubble Space Telescope (HST) ultraviolet and ground-based optical observations of the hot, metal-rich white dwarf GD 394. Extreme-ultraviolet (EUV) observations in 1992-1996 revealed a 1.15d periodicity with a 25 percent amplitude, hypothesised to be due to metals in a surface accretion spot. We obtained phase-resolved HST/Space Telescope Imaging Spectrograph (STIS) high-resolution far-ultraviolet (FUV) spectra of GD 394 that sample the entire period, along with a large body of supplementary data. We find no evidence for an accretion spot, with the flux, accretion rate and radial velocity of GD 394 constant over the observed timescales at ultraviolet and optical wavelengths. We speculate that the spot may have no longer been present when our observations were obtained, or that the EUV variability is being caused by an otherwise undetected evaporating planet. The atmospheric parameters obtained from separate fits to optical and ultraviolet spectra are inconsistent, as is found for multiple hot white dwarfs. We also detect non-photospheric, high-excitation absorption lines of multiple volatile elements, which could be evidence for a hot plasma cocoon surrounding the white dwarf
NGTS and HST insights into the long period modulation in GW Librae
Light curves of the accreting white dwarf pulsator GW Librae spanning a 7.5
month period in 2017 were obtained as part of the Next Generation Transit
Survey. This data set comprises 787 hours of photometry from 148 clear nights,
allowing the behaviour of the long (hours) and short period (20min) modulation
signals to be tracked from night to night over a much longer observing baseline
than has been previously achieved. The long period modulations intermittently
detected in previous observations of GW Lib are found to be a persistent
feature, evolving between states with periods ~83min and 2-4h on time-scales of
several days. The 20min signal is found to have a broadly stable amplitude and
frequency for the duration of the campaign, but the previously noted phase
instability is confirmed. Ultraviolet observations obtained with the Cosmic
Origin Spectrograph onboard the Hubble Space Telescope constrain the
ultraviolet-to-optical flux ratio to ~5 for the 4h modulation, and <=1 for the
20min period, with caveats introduced by non-simultaneous observations. These
results add further observational evidence that these enigmatic signals must
originate from the white dwarf, highlighting our continued gap in theoretical
understanding of the mechanisms that drive them