Leo Huckvale

The second data release of the INT Photometric Hα 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 catalogues 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.

Spatio-kinematic modelling of Abell 65, a double-shelled planetary nebula with a binary central star

We present the first detailed spatio-kinematical analysis and modelling of the planetary nebula Abell 65, which is known to host a post-common envelope, binary, central star system. As such, this object is of great interest in studying the link between nebular morphology and central star binarity. [O III]5007 A and Hα+[N II]6584 A longslit spectra and imagery of Abell 65 were obtained with the Manchester Echelle Spectrometer on the 2.1-m telescope at the San Pedro Martir Observatory (MES-SPM). Further [O III]5007 A longslit spectra were obtained with the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope (VLT-UVES). These data were used to develop a spatio-kinematical model for the [O III]5007 A emission from Abell 65. A ‘best-fitting’ model was found by comparing synthetic spectra and images rendered from the model to the data. The model comprises an outer shell and an inner shell, with kinematical ages of 15000 ± 5000 yr kpc−1 and 8000 ± 3000 yr kpc−1, respectively. Both shells have peanut-shaped bipolar structures with symmetry axes at inclinations of (55 ± 10)° (to the line of sight) for the outer shell and (68 ± 10)° for the inner shell. The near alignment between the nebular shells and the binary orbital inclination [of (68 ± 2)°] is strongly indicative that the binary is responsible for shaping the nebula. Abell 65 is one of a growing number of planetary nebulae (seven to date, including Abell 65 itself) for which observations and modelling support the shaping influence of a central binary.

Asking gender questions: Results from a survey of gender and question asking among UK Astronomers at NAM2014

Jonathan Pritchard, Karen Masters, James Allen, Filippo Contenta, Leo Huckvale, Stephen Wilkins and Alice Zocchi report on a survey of the gender of astronomers attending and asking questions at this years UK National Astronomy Meeting.

Reference image selection for difference imaging analysis

Difference image analysis (DIA) is an effective technique for obtaining photometry in crowded fields, relative to a chosen reference image. As yet, however, optimal reference image selection is an unsolved problem. We examine how this selection depends on the combination of seeing, background and detector pixel size. Our tests use a combination of simulated data and quality indicators from DIA of well-sampled optical data and under-sampled near-infrared data from the Optical Gravitational Lensing Experiment and VVV surveys, respectively. We search for a figure-of-merit (FoM) which could be used to select reference images for each survey. While we do not find a universally applicable FoM, survey-specific measures indicate that the effect of spatial under-sampling may require a change in strategy from the standard DIA approach, even though seeing remains the primary criterion. We find that background is not an important criterion for reference selection, at least for the dynamic range in the images we test. For our analysis of VVV data in particular, we find that spatial under-sampling is best handled by reversing the standard DIA procedure and convolving target images to a better-sampled (poor-seeing) reference image.

Asking gender questions

Jonathan Pritchard, Karen Masters, James Allen, Filippo Contenta, Leo Huckvale, Stephen Wilkins and Alice Zocchi report on a survey of the gender of astronomers attending and asking questions at this years UK National Astronomy Meeting.

Asking gender questionsGender at NAM

Jonathan Pritchard, Karen Masters, James Allen, Filippo Contenta, Leo Huckvale, Stephen Wilkins and Alice Zocchi report on a survey of the gender of astronomers attending and asking questions at this years UK National Astronomy Meeting.

Stellar variability in the VVV survey : Overview and first results

The Vista Variables in the V´oa Lactea (VVV) ESO Public Survey is an ongoing time-series, near-infrared (IR) survey of the Galactic bulge and an adjacent portion of the inner disk, covering 562 square degrees of the sky, using ESOs VISTA telescope. The survey has provided su- perb multi-color photometry in 5 broadband filters (Z, Y , J, H, and Ks), leading to the best map of the inner Milky Way ever obtained, par- ticularly in the near-IR. The main variability part of the survey, which is focused on Ks-band observations, is currently underway, with bulge fields having been observed between 31 and 70 times, and disk fields be- tween 17 and 36 times. When the survey is complete, bulge (disk) fields