The limit order book on different time scales

Financial markets can be described on several time scales. We use data from the limit order book of the London Stock Exchange (LSE) to compare how the fluctuation dominated microstructure crosses over to a more systematic global behavior.Comment: 11 pages, 7 figures, 2 tables, to appear in Proc. SPIE, Fluctuations and Noise 2007, Florenc

Close binary central stars and the abundance discrepancy - new extreme objects

Recent work (Corradi et al. 2015, Jones et al. 2016) has shown that the phenomenon of extreme abundance discrepancies, where recombination line abundances exceed collisionally excited line abundances by factors of 10 or more, seem to be strongly associated with planetary nebulae with close binary central stars. To further investigate, we have obtained spectra of a sample of nebulae with known close binary central stars, using FORS2 on the VLT, and we have discovered several new extreme abundance discrepancy objects. We did not find any non-extreme discrepancies, suggesting that a very high fraction of nebulae with close binary central stars also have an extreme abundance discrepancy

Confirmation of the link between central star binarity and extreme abundance discrepancy factors in planetary nebulae

It has recently been noted that there seems to be a strong correlation between planetary nebulae with close binary central stars and highly enhanced recombination line abundances. We present new deep spectra of seven objects known to have close binary central stars, and find that the heavy element abundances derived from recombination lines exceed those from collisionally excited lines by factors of 5–95, placing several of these nebulae among the most extreme known abundance discrepancies. This study nearly doubles the number of nebulae known to have a binary central star and an extreme abundance discrepancy. A statistical analysis of all nebulae with measured recombination line abundances reveals no link between central star surface chemistry and nebular abundance discrepancy, but a clear link between binarity and the abundance discrepancy, as well as an anticorrelation between abundance discrepancies and nebular electron densities: all nebulae with a binary central star with a period of less than 1.15 d have an abundance discrepancy factor exceeding 10, and an electron density less than ∼1000 cm−3; those with longer period binaries have abundance discrepancy factors less than 10 and much higher electron densities. We find that [O II] density diagnostic lines can be strongly enhanced by recombination excitation, while [S II] lines are not. These findings give weight to the idea that extreme abundance discrepancies are caused by a nova-like eruption from the central star system, occuring soon after the common-envelope phase, which ejects material depleted in hydrogen, and enhanced in CNONe but not in third-row elements

MUSE spectroscopy of planetary nebulae with high abundance discrepancies

We present MUSE deep integral-field unit spectroscopy of three planetary nebulae(PNe) with high abundance discrepancy factors (ADF > 20): NGC 6778, M 1-42 and Hf 2-2. We have constructed flux maps for more than 40 emission lines, and use them to build extinction, electron temperature (T$_e$), electron density (n$_e$), and ionic abundances maps of a number of ionic species. The effects of the contribution of recombination to the auroral [N II] and [O II] lines on T$_e$ and the abundance maps of low-ionization species are evaluated using recombination diagnostics. As a result, low T$_e$ values and a downward gradient of T$_e$ are found toward the inner zones of each PN. Spatially, this nearly coincides with the increase of abundances of heavy elements measured using recombination lines in the inner regions of PNe, and strongly supports the presence of two distinct gas phases: a cold and metal-rich and a warm one with "normal" metal content. We have simultaneously constructed, for the first time, the ADF maps of O$^+$ and O$^{2+}$ and found that they centrally peak for all three PNe under study. We show that the main issue when trying to compute realistic abundances from either ORLs or CELs is to estimate the relative contribution of each gas component to the H I emission, and we present a method to evaluate it. It is also found that, for the studied high-ADF PNe, the amount of oxygen in the cold and warm regions is of the same order

MUSE spectroscopy of planetary nebulae with high abundance discrepancies

We present MUSE deep integral-field unit spectroscopy of three planetary nebulae(PNe) with high abundance discrepancy factors (ADF > 20): NGC 6778, M 1-42 and Hf 2-2. We have constructed flux maps for more than 40 emission lines, and use them to build extinction, electron temperature (T$_e$), electron density (n$_e$), and ionic abundances maps of a number of ionic species. The effects of the contribution of recombination to the auroral [N II] and [O II] lines on T$_e$ and the abundance maps of low-ionization species are evaluated using recombination diagnostics. As a result, low T$_e$ values and a downward gradient of T$_e$ are found toward the inner zones of each PN. Spatially, this nearly coincides with the increase of abundances of heavy elements measured using recombination lines in the inner regions of PNe, and strongly supports the presence of two distinct gas phases: a cold and metal-rich and a warm one with "normal" metal content. We have simultaneously constructed, for the first time, the ADF maps of O$^+$ and O$^{2+}$ and found that they centrally peak for all three PNe under study. We show that the main issue when trying to compute realistic abundances from either ORLs or CELs is to estimate the relative contribution of each gas component to the H I emission, and we present a method to evaluate it. It is also found that, for the studied high-ADF PNe, the amount of oxygen in the cold and warm regions is of the same order

AT 2019abn: multi-wavelength observations of the first 200 days

AT 2019abn was discovered in the nearby M51 galaxy, by the Zwicky Transient Facility more than two magnitudes, and around 3 weeks, prior to its optical peak. We aimed to conduct a detailed photometric and spectroscopic follow-up campaign for AT 2019abn, with the early discovery allowing significant pre-maximum observations of an intermediate luminosity red transient (ILRT) for the first time. This work is based around the analysis of u'BVr'i'z'H photometry and low-resolution spectroscopy with the Liverpool Telescope, medium-resolution spectroscopy with Gran Telescopio Canarias (GTC) and near-infrared imaging with GTC and the Nordic Optical Telescope. We present the most detailed optical light curve of an ILRT to date, with multi-band photometry starting around three weeks before peak brightness. The transient peaked at an observed absolute magnitude of M_r=-13.1, although it is subject to significant reddening from dust in M51, implying an intrinsic M_r~-15.2. The initial light curve showed a linear, achromatic rise in magnitude, before becoming bluer at peak. After peak brightness the transient gradually cooled. This is reflected in our spectra which at later times show absorption from species such as Fe I, Ni I and Li I. A spectrum taken around peak brightness shows narrow, low-velocity absorption lines, which we interpret as likely originating from pre-existing circumstellar material. We conclude that, while there are some peculiarities, such as the radius evolution, AT 2019abn overall fits in well with the ILRT class of objects, and is the most luminous member of the class seen to date

The post-common-envelope binary central star of the planetary nebula PN G283.7-05.1

We present the discovery and characterisation of the post-common-envelope central star system in the planetary nebula PN G283.7-05.1. Deep images taken as part of the POPIPlaN survey indicate that the nebula may possess a bipolar morphology similar to other post-common-envelope planetary nebulae. Simultaneous light and radial velocity curve modelling reveals that the newly discovered binary system comprises a highly irradiated M-type main-sequence star in a 5.9-hour orbit with a hot pre-white dwarf. The nebular progenitor is found to have a particularly low mass of around 0.4 M, making PN G283.7-05.1 one of only a handful of candidate planetary nebulae that is the product of a common-envelope event while still on the red giant branch. In addition to its low mass, the model temperature, surface gravity, and luminosity are all found to be consistent with the observed stellar and nebular spectra through comparison with model atmospheres and photoionisation modelling. However, the high temperature (Teff ∼ 95 kK) and high luminosity of the central star of the nebula are not consistent with post-RGB evolutionary tracks

Imaging the elusive H-poor gas in planetary nebulae with large abundance discrepancy factors

The discrepancy between abundances computed using optical recombination lines (ORLs) and collisionally excited lines (CELs) is a major, unresolved problem with significant implications for the determination of chemical abundances throughout the Universe. In planetary nebulae (PNe), the most common explanation for the discrepancy is that two different gas phases coexist: a hot component with standard metallicity, and a much colder plasma enhanced in heavy elements. This dual nature is not predicted by mass loss theories, and direct observational support for it is still weak. In this work, we present our recent findings that demonstrate that the largest abundance discrepancies are associated with close binary central stars. OSIRIS-GTC tunable filter imaging of the faint O II ORLs and MUSE-VLT deep 2D spectrophotometry confirm that O II ORL emission is more centrally concentrated than that of [O III] CELs and, therefore, that the abundance discrepancy may be closely linked to binary evolution

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

Rotation Curves of Spiral Galaxies

Rotation curves of spiral galaxies are the major tool for determining the distribution of mass in spiral galaxies. They provide fundamental information for understanding the dynamics, evolution and formation of spiral galaxies. We describe various methods to derive rotation curves, and review the results obtained. We discuss the basic characteristics of observed rotation curves in relation to various galaxy properties, such as Hubble type, structure, activity, and environment.Comment: 40 pages, 6 gif figures; Ann. Rev. Astron. Astrophys. Vol. 39, p.137, 200