We present high-resolution infrared (2–18 μm) images of the archetypal periodic dust-making Wolf–Rayet binary system WR 140 (HD 193793) taken between 2001 and 2005, and multi-colour (J–19.5) ...photometry observed between 1989 and 2001. The images resolve the dust cloud formed by WR 140 in 2001, allowing us to track its expansion and cooling, while the photometry allows tracking the average temperature and total mass of the dust. The combination of the two data sets constrains the optical properties of the dust, and suggests that they differ from those of the dust made by the WC9 dust-makers, including the classical ‘pinwheel’, WR 104. The photometry of individual dust emission features shows them to be significantly redder in (nbL′–3.99), but bluer in (7.9–12.5), than the binary, as expected from the spectra of heated dust and the stellar wind of a Wolf–Rayet star. The most persistent dust features, two concentrations at the ends of a ‘bar’ of emission to the south of the star, were observed to move with constant proper motions of 324 ± 8 and 243 ± 7 mas yr−1. Longer wavelength (4.68 and 12.5 μm) images show dust emission from the corresponding features from the previous (1993) periastron passage and dust formation episode, showing that the dust expanded freely in a low-density void for over a decade, with dust features repeating from one cycle to the next. A third persistent dust concentration to the east of the binary (the ‘arm’) was found to have a proper motion ∼320 mas yr−1, and a dust mass about one-quarter that of the ‘bar’. Extrapolation of the motions of the concentrations back to the binary suggests that the eastern ‘arm’ began expansion four to five months earlier than those in the southern ‘bar’, consistent with the projected rotation of the binary axis and wind-collision region (WCR) on the sky. A comparison of model dust images and the observations constrains the intervals when the WCR was producing sufficiently compressed wind for dust nucleation in the WCR, and suggests that the distribution of this material was not uniform about the axis of the WCR, but more abundant in the following edge in the orbital plane.
ABSTRACT
OJ 287 is a BL Lacertae type quasar in which the active galactic nucleus (AGN) outshines the host galaxy by an order of magnitude. The only exception to this may be at minimum light when the ...AGN activity is so low that the host galaxy may make quite a considerable contribution to the photometric intensity of the source. Such a dip or a fade in the intensity of OJ 287 occurred in 2017 November, when its brightness was about 1.75 mag lower than the recent mean level. We compare the observations of this fade with similar fades in OJ 287 observed earlier in 1989, 1999, and 2010. It appears that there is a relatively strong reddening of the B− V colours of OJ 287 when its V-band brightness drops below magnitude 17. Similar changes are also seen in V− R, V− I, and R− I colours during these deep fades. These data support the conclusion that the total magnitude of the host galaxy is V = 18.0 ± 0.3, corresponding to MK = −26.5 ± 0.3 in the K-band. This is in agreement with the results, obtained using the integrated surface brightness method, from recent surface photometry of the host. These results should encourage us to use the colour separation method also in other host galaxies with strongly variable AGN. In the case of OJ 287, both the host galaxy and its central black hole are among the biggest known, and its position in the black hole mass–galaxy mass diagram lies close to the mean correlation.
Aims. The blazar OJ 287 had its biggest optical outburst in over 20 years. It occurred in October/November 2005 and was somewhat expected since similar outbursts had occurred at approximately 12 yr ...intervals since the early 1900s. However, a strict periodicity would have put the event nearly a year later. Here we ask whether the October/November 2005 outburst was indeed the expected 2006 outburst of OJ287. Did it follow the typical light curve behaviour of such events: a rapid initial rise in just over a week and a slower decay in the following months? Methods. In this study we use the extensive observations of The British Astronomical Association Variable Star Section, complemented by the data from The American Association of Variable Star Observers. We compare the 2005 outburst with the previous season's first peak of 1983. Results. We find that the beginning of the 2005 outburst occurred at 2005.76, a few weeks earlier than was reported previously. The timing of the outburst is consistent with the binary black hole model of Lehto and Valtonen. In accordance with this model, we find that the outburst's structural time scale is slower in 2005 than in 1983, while the 2005 outburst was fainter than the 1983 outburst, making the two outbursts about equal in energy. Thus it is quite reasonable to argue that the 2005 outburst was the expected first of the season in the optical light curve of OJ287.
The thermal emission of comet C/2013 A1 (Siding Spring) was observed on March 31, 2013, at a heliocentric distance of 6.48 au using the PACS photometer camera of the Herschel Space Observatory. The ...comet was clearly active, showing a coma that could be traced to a distance of ~10′′, i.e. ~50 000 km. Analysis of the radial intensity profiles of the coma provided a dust mass and dust production rate and the derived grain size distribution characteristics indicate an overabundance of large grains in the thermal emission. We estimate that activity started about 6 months before these observations at a heliocentric distance of ~8 au.
Prior to and around the Rosetta flyby of (21) Lutetia, the Herschel Space Observatory performed a collaborative observation campaign with its two photometers observing the asteroid in the far ...infrared, at wavelengths not covered by Rosetta’s instruments. The Herschel observations, fed into a thermophysical model (TPM) using as input a shape model based on in-situ images, were also further correlated with ∼70 multi-wavelength observations of Lutetia. We confirm the geometric albedo measured by Rosetta, derive a H-mag value based upon the effective diameter of the asteroid and point to (21) Lutetia having an extremely low thermal inertia (5Jm−2s−0.5K−1). This thermal inertia is only possible through the existence of a significant amount of small scale roughness which is not directly observable by the OSIRIS (Optical, Spectroscopic, and Infrared Imaging System) instrument on-board Rosetta. In addition, our results point to the existence of a hill/crater surface feature located on the asteroids southern region not observed by Rosetta. From our results, we conclude that only through the merging of in situ and remote sensing observations can a true global picture be obtained of this asteroid.
► We provide Herschel observations (PACS & SPIRE photometer) of (21) Lutetia. ► We derive values for H-Mag and Albedo of (21) Lutetia. ► We find (21) Lutetia has a very low Thermal inertia (5Jm−2s−0.5K−1). ► We identify a hill/crater surface feature on the (21) Lutetia not observed by Rosetta
176P/LINEAR is a member of the new cometary class known as main-belt comets (MBCs). It displayed cometary activity shortly during its 2005 perihelion passage, which may be driven by the sublimation ...of subsurface ices. We have therefore searched for emission of the H2O 110–101 ground state rotational line at 557 GHz toward 176P/LINEAR with the Heterodyne Instrument for the Far Infrared (HIFI) onboard the Herschel Space Observatory on UT 8.78 August 2011, about 40 days after its most recent perihelion passage, when the object was at a heliocentric distance of 2.58 AU. No H2O line emission was detected in our observations, from which we derive sensitive 3-σ upper limits for the water production rate and column density of <4 × 1025 mol s-1 and of <3 × 1010 cm-2, respectively. From the peak brightness measured during the object’s active period in 2005, this upper limit is lower than predicted by the relation between production rates and visual magnitudes observed for a sample of comets at this heliocentric distance. Thus, 176P/LINEAR was most likely less active at the time of our observation than during its previous perihelion passage. The retrieved upper limit is lower than most values derived for the H2O production rate from the spectroscopic search for CN emission in MBCs.
We report on the initial analysis of a Herschel-PACS full range spectrum of Neptune, covering the 51–220 μm range with a mean resolving power of ~3000, and complemented by a dedicated observation of ...CH4 at 120 μm. Numerous spectral features due to HD (R(0) and R(1)), H2O, CH4, and CO are present, but so far no new species have been found. Our results indicate that (i) Neptune's mean thermal profile is warmer by ~3 K than inferred from the Voyager radio-occultation; (ii) the D/H mixing ratio is (4.5 ± 1) × 10-5, confirming the enrichment of Neptune in deuterium over the protosolar value (~2.1 × 10-5); (iii) the CH4 mixing ratio in the mid stratosphere is (1.5 ± 0.2) × 10-3, and CH4 appears to decrease in the lower stratosphere at a rate consistent with local saturation, in agreement with the scenario of CH4 stratospheric injection from Neptune's warm south polar region; (iv) the H2O stratospheric column is (2.1 ± 0.5) × 1014 cm-2 but its vertical distribution is still to be determined, so the H2O external flux remains uncertain by over an order of magnitude; and (v) the CO stratospheric abundance is about twice the tropospheric value, confirming the dual origin of CO suspected from ground-based millimeter/submillimeter observations.
Context. The goal of the Herschel open time programme “TNOs are Cooll” is to derive the physical and thermal properties for a large sample of Centaurs, and trans-Neptunian objects (TNOs), including ...resonant, classical, detached and scattered disk objects. Aims. Based on observations of two targets we tried (i) to optimise the SPIRE observing technique for faint (close to the background confusion noise), slowly moving targets; (ii) to test different thermal model techniques; (iii) to determine radiometric diameter and albedo values; (iv) to compare with Spitzer results whenever possible. Methods. We obtained SPIRE photometry on two targets and PACS photometry on one of the targets. Results. We present results for the two targets, (90482) Orcus and (136472) Makemake, observed with SPIRE and for one of those targets, Makemake, observed with PACS. We adopt pv = 0.27 and D = 850 km as our best estimate of the albedo and diameter of Orcus using single terrain models. With two-terrain models for Makemake, the bright terrain is fitted by, 0.78 \textless pv \textless 0.90, and the dark terrain 0.02 \textless pv \textless 0.12, giving 1360 \textless D \textless 1480 km. Conclusions. A single terrain model was derived for Orcus through the SPIRE photometry combined with MIPS data. The Makemake data from MIPS, PACS and SPIRE combined are not compatible with a single terrain model, but can be modelled with a two-terrain fit. These science demonstration observations have shown that the scanning technique, which allows us to judge the influence of background structures, has proved to be a good basis for this key programme.
The Jupiter-family comet 10P/Tempel 2 was observed during its 2010 return with the Herschel Space Observatory. We present here the observation of the JK (10–00) transition of NH3 at 572 GHz in this ...comet with the Heterodyne Instrument for the Far Infrared (HIFI) of Herschel. We also report on radio observations of other molecules (HCN, CH3OH, H2S and CS) obtained during the 1999 return of the comet with the CSO telescope and the JCMT, and during its 2010 return with the IRAM 30-m telescope. Molecular abundances relative to water are 0.09%, 1.8%, 0.4%, and 0.08% for HCN, CH3OH, H2S, and CS, respectively. An abundance of 0.5% for NH3 is obtained, which is similar to the values measured in other comets. The hyperfine structure of the ammonia line is resolved for the first time in an astronomical source. Strong anisotropy in the outgassing is present in all observations from 1999 to 2010 and is modelled to derive the production rates.
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