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This paper presents a study of circumstellar debris around Sun-like stars using data from the Herschel DEBRIS Key Programme. DEBRIS is an unbiased survey comprising the nearest ∼90 stars of each spectral type A-M. Analysis of the 275 F-K stars shows that excess emission from a debris disc was detected around 47 stars, giving a detection rate of 17.1+2.6-2.3 per cent, with lower rates for later spectral types. For each target a blackbody spectrum was fitted to the dust emission to determine its fractional luminosity and temperature. The derived underlying distribution of fractional luminosity versus blackbody radius in the population showed that most detected discs are concentrated at f∼10-5 and at temperatures corresponding to blackbody radii 7-40 au, which scales to ∼40 au for realistic dust properties (similar to the current Kuiper belt). Two outlying populations are also evident; five stars have exceptionally bright emission ( f > 5 × 10-5), and one has unusually hot dust <4 au. The excess emission distributions at all wavelengths were fitted with a steady-state evolution model, showing that these are compatible with all stars being born with a narrow belt that then undergoes collisional grinding. However, the model cannot explain the hot dust systems - likely originating in transient events - and bright emission systems - arising potentially from atypically massive discs or recent stirring. The emission from the present-day Kuiper belt is predicted to be close to the median of the population, suggesting that half of stars have either depleted their Kuiper belts (similar to the Solar system) or had a lower planetesimal formation efficiency. [ABSTRACT FROM AUTHOR]

Lambda Boo stars are predominately A-type stars with solar abundant C, N, O, and S, but up to 2 dex underabundances of refractory elements. The stars' unusual surface abundances could be due to a selective accretion of volatile gas over dust. It has been proposed that there is a correlation between the Lambda Boo phenomenon and IR excesses which are the result of a debris disc or interstellar medium (ISM) interaction providing the accreting material. We observe 70 or 100 and 160-μm excess emission around nine confirmed Lambda Boo stars with the Herschel Space Observatory, to differentiate whether the dust emission is from a debris disc or an ISM bow wave. We find that 3/9 stars observed host well-resolved debris discs. While the remaining 6/9 are not resolved; they are inconsistent with an ISM bow wave based on the dust emission being more compact for its temperature and predicted bow-wave models produce hotter emission than what is observed. We find the incidence of bright IR excesses around Lambda Boo stars is higher than normal A-stars. To explain this, given our observations, we explore Poynting-Robertson drag as a mechanism of accretion from a debris disc but find it insufficient. As an alternative, we propose the correlation is due to higher dynamical activity in the discs currently underway. Large impacts of planetesimals or a higher influx of comets could provide enough volatile gas for accretion. Further study on the transport of circumstellar material in relation to the abundance anomalies are required to explain the phenomenon through external accretion. [ABSTRACT FROM AUTHOR]

The Herschel DEBRIS (Disc Emission via a Bias-free Reconnaissance in the Infrared/Submillimetre) survey brings us a unique perspective on the study of debris discs around main-sequence A-type stars. Bias-free by design, the survey offers a remarkable data set with which to investigate the cold disc properties. The statistical analysis of the 100 and 160 μm data for 86 main-sequence A stars yields a lower than previously found debris disc rate. Considering better than 3σ excess sources, we find a detection rate ≥24 ± 5 per cent at 100 μm which is similar to the debris disc rate around main-sequence F/G/K-spectral type stars. While the 100 and 160 μm excesses slowly decline with time, debris discs with large excesses are found around some of the oldest A stars in our sample, evidence that the debris phenomenon can survive throughout the length of the main sequence (∼1 Gyr). Debris discs are predominantly detected around the youngest and hottest stars in our sample. Stellar properties such as metallicity are found to have no effect on the debris disc incidence. Debris discs are found around A stars in single systems and multiple systems at similar rates. While tight and wide binaries (<1 and >100 au, respectively) host debris discs with a similar frequency and global properties, no intermediate separation debris systems were detected in our sample. [ABSTRACT FROM AUTHOR]

τ Ceti is a nearby, mature G-type star very similar to our Sun, with a massive Kuiper Belt analogue and possible multiplanet system that has been compared to our Solar system. We present Herschel Space Observatory images of the debris disc, finding the disc is resolved at 70 μm and 160 μm, and marginally resolved at 250 μm. The Herschel images and infrared photometry from the literature are best modelled using a wide dust annulus with an inner edge between 1 and 10 au and an outer edge at ∼55 au, inclined from face-on by 35° ± 10°, and with no significant azimuthal structure. We model the proposed tightly packed planetary system of five super-Earths and find that the innermost dynamically stable disc orbits are consistent with the inner edge found by the observations. The photometric modelling, however, cannot rule out a disc inner edge as close to the star as 1 au, though larger distances produce a better fit to the data. Dynamical modelling shows that the five-planet system is stable with the addition of a Neptune or smaller mass planet on an orbit outside 5 au, where the radial velocity data analysis would not have detected a planet of this mass. [ABSTRACT FROM AUTHOR]

ALMA Cycle 0 and Herschel1 PACS observations are reported for the prototype, nearest, and brightest example of a dusty and polluted white dwarf, G29-38. These long-wavelength programmes attempted to detect an outlying, parent population of bodies at 1–100 au, from which originates the disrupted planetesimal debris that is observed within 0.01 au and which exhibits LIR/L* = 0.039. No associated emission sources were detected in any of the data down to LIR/L* ∼ 10−4, generally ruling out cold dust masses greater than 1024–1025 g for reasonable grain sizes and properties in orbital regions corresponding to evolved versions of both asteroid and Kuiper belt analogues. Overall, these null detections are consistent with models of long-term collisional evolution in planetesimal discs, and the source regions for the disrupted parent bodies at stars like G29-38 may only be salient in exceptional circumstances, such as a recent instability. A larger sample of polluted white dwarfs, targeted with the full ALMA array, has the potential to unambiguously identify the parent source(s) of their planetary debris. [ABSTRACT FROM PUBLISHER]

Context. Stars form surrounded by gas- and dust-rich protoplanetary discs. Generally, these discs dissipate over a few (3–10) Myr, leaving a faint tenuous debris disc composed of second-generation dust produced by the attrition of larger bodies formed in the protoplanetary disc. Giant planets detected in radial velocity and transit surveys of main-sequence stars also form within the protoplanetary disc, whilst super-Earths now detectable may form once the gas has dissipated. Our own solar system, with its eight planets and two debris belts, is a prime example of an end state of this process. Aims. The Herschel DEBRIS, DUNES, and GT programmes observed 37 exoplanet host stars within 25 pc at 70, 100, and 160 μm with the sensitivity to detect far-infrared excess emission at flux density levels only an order of magnitude greater than that of the solar system’s Edgeworth-Kuiper belt. Here we present an analysis of that sample, using it to more accurately determine the (possible) level of dust emission from these exoplanet host stars and thereafter determine the links between the various components of these exoplanetary systems through statistical analysis. Methods. We have fitted the flux densities measured from recent Herschel observations with a simple two parameter (Td, LIR/L⋆) black-body model (or to the 3σ upper limits at 100 μm). From this uniform approach we calculated the fractional luminosity, radial extent and dust temperature. We then plotted the calculated dust luminosity or upper limits against the stellar properties, e.g. effective temperature, metallicity, and age, and identified correlations between these parameters. Results. A total of eleven debris discs are identified around the 37 stars in the sample. An incidence of ten cool debris discs around the Sun-like exoplanet host stars (29 ± 9%) is consistent with the detection rate found by DUNES (20.2 ± 2.0%). For the debris disc systems, the dust temperatures range from 20 to 80 K, and fractional luminosities (LIR/L⋆) between 2.4 ×10−6 and 4.1 ×10−4. In the case of non-detections, we calculated typical 3σ upper limits to the dust fractional luminosities of a few ×10−6. Conclusions. We recover the previously identified correlation between stellar metallicity and hot-Jupiter planets in our data set.We find a correlation between the increased presence of dust, lower planet masses, and lower stellar metallicities. This confirms the recently identified correlation between cold debris discs and low-mass planets in the context of planet formation by core accretion. [ABSTRACT FROM AUTHOR]

Context. The dusty debris disk around the ~20 Myr old main-sequence A-star β Pictoris is known to contain gas. Evidence points towards a secondary origin of the gas as opposed to being a direct remnant from the initial protoplanetary disk, although the dominant gas production mechanism is so far not identified. The origin of the observed overabundance of C and O compared with solar abundances of metallic elements such as Na and Fe is also unclear. Aims. Our goal is to constrain the spatial distribution of C in the disk, and thereby the gas origin and its abundance pattern. Methods. We used the HIFI instrument on board the Herschel Space Observatory to observe and spectrally resolve C ii emission at 158 μm from the β Pic debris disk. Assuming a disk in Keplerian rotation and a model for the line emission from the disk, we used the spectrally resolved line profile to constrain the spatial distribution of the gas. Results. We detect the Cii 158 μm emission. Modelling the shape of the emission line shows that most of the gas is located at about ~100 AU or beyond. We estimate a total C gas mass of 1:3+1:3 -0:5 ~ 10-2 M⊗ (central 90% confidence interval). The data suggest that more gas is located on the south-west side of the disk than on the north-east side. The shape of the emission line is consistent with the hypothesis of a well mixed gas (constant C/Fe ratio throughout the disk). Assuming instead a spatial profile expected from a simplified accretion disk model, we found it to give a significantly poorer fit to the observations. Conclusions. Since the bulk of the gas is found outside 30 AU, we argue that the cometary objects known as "falling evaporating bodies" are probably not the dominant source of gas; production from grain-grain collisions or photodesorption seems more likely. The incompatibility of the observations with a simplified accretion disk model might favour a preferential depletion explanation for the overabundance of C and O, although it is unclear how much this conclusion is affected by the simplifications made. More stringent constraints on the spatial distribution will be available from ALMA observations of Ci emission at 609 μm. [ABSTRACT FROM AUTHOR]

Debris disks have been found primarily around intermediate and solar mass stars (spectral types A-K) but rarely around low mass M-type stars. We have spatially resolved a debris disk around the remarkable M3-type star GJ 581 hosting multiple planets using deep PACS images at 70, 100 and 160 μm as part of the DEBRIS Program on the Herschel Space Observatory. This is the second spatially resolved debris disk found around an M-type star, after the one surrounding the young star AU Mic (12 Myr). However, GJ 581 is much older (2-8 Gyr), and is X-ray quiet in the ROSAT data. We fit an axisymmetric model of the disk to the three PACS images and found that the best fit model is for a disk extending radially from 25 ± 12 AU to more than 60 AU. Such a cold disk is reminiscent of the Kuiper belt but it surrounds a low mass star (0.3 M☉) and its fractional dust luminosity Ldust/L of ∼10-4 is much higher. The inclination limits of the disk found in our analysis make the masses of the planets small enough to ensure the long-term stability of the system according to some dynamical simulations. The disk is collisionally dominated down to submicron-sized grains and the dust cannot be expelled from the system by radiation or wind pressures because of the low luminosity and low X-ray luminosity of GJ 581. We suggest that the correlation between low-mass planets and debris disks recently found for G-type stars also applies to M-type stars. Finally, the known planets, of low masses and orbiting within 0.3 AU from the star, cannot dynamically perturb the disk over the age of the star, suggesting that an additional planet exists at larger distance that is stirring the disk to replenish the dust. [ABSTRACT FROM AUTHOR]

ABSTRACT We present resolved Herschel images of circumbinary debris discs in the α CrB (HD 139006) and β Tri (HD13161) systems. By modelling their structure, we find that both discs are consistent with being aligned with the binary orbital planes. Though secular perturbations from the binary can bring the disc into alignment, in both cases the alignment time at the distances at which the disc is resolved is greater than the stellar age, so we conclude that the coplanarity was primordial. Neither disc can be modelled as a narrow ring, requiring extended radial distributions. To satisfy both the Herschel and mid-infrared images of the α CrB disc, we construct a model that extends from 1 to 300 au, whose radial profile is broadly consistent with a picture where planetesimal collisions are excited by secular perturbations from the binary. However, this model is also consistent with stirring by other mechanisms, such as the formation of Pluto-sized objects. The β Tri disc is modelled as a disc that extends from 50 to 400 au. A model with depleted (rather than empty) inner regions also reproduces the observations and is consistent with binary and other stirring mechanisms. As part of the modelling process, we find that the Herschel PACS (Photodetector and Array Camera & Spectrometer) beam varies by as much as 10 per cent at 70 μm and a few per cent at 100 μm. The 70 μm variation can therefore hinder image interpretation, particularly for poorly resolved objects. The number of systems in which circumbinary debris disc orientations have been compared with the binary plane is now 4. More systems are needed, but a picture in which discs around very close binaries (α CrB, β Tri and HD 98800, with periods of a few weeks to a year) are aligned, and discs around wider binaries (99 Her, with a period of 50 yr) are misaligned, may be emerging. This picture is qualitatively consistent with the expectation that the protoplanetary discs from which the debris emerged are more likely to be aligned if their binaries have shorter periods. [ABSTRACT FROM AUTHOR]

CW Leo has been observed six times between October 2009 and June 2012 with the SPIRE instrument on board the Herschel satellite. Variability has been detected in the flux emitted by the central star with a period of 639 ± 4 days, in good agreement with determinations in the literature. Variability is also detected in the bow shock around CW Leo that had previously been detected in the ultraviolet and Herschel PACS/SPIRE data. Although difficult to prove directly, our working hypothesis is that this variability is directly related to that of the central star. In this case, fitting a sine curve with the period fixed to 639 days results in a time-lag in the variability between bow shock and the central star of 402 ± 37 days. The orientation of the bow shock relative to the plane of the sky is unknown (but see below). For an inclination angle of zero degrees, the observed time-lag translates into a distance to CW Leo of 130 ± 13 pc, and for non-zero inclination angles the distance is smaller. Fitting the shape of the bow shock with an analytical model (Wilkin 1996, ApJ, 459, L31), the effect of the inclination angle on the distance may be estimated. Making the additional assumption that the relative peculiar velocity between the interstellar medium (ISM) and CW Leo is determined entirely by the star space velocity with respect to the local standard of rest (i.e. a stationary ISM), the inclination angle is found to be (-33.3 ± 0.8)° based on the observed proper motion and radial velocity. Using the Wilkin model, our current best estimate of the distance to CW Leo is 123 ± 14 pc. For a distance of 123 pc, we derive a mean luminosity of 7790 ± 150 L⊙ (internal error). [ABSTRACT FROM AUTHOR]

ABSTRACT We present resolved Herschel images of a circumbinary debris disc in the 99 Herculis system. The primary is a late F-type star. The binary orbit is well characterized and we conclude that the disc is misaligned with the binary plane. Two different models can explain the observed structure. The first model is a ring of polar orbits that move in a plane perpendicular to the binary pericentre direction. We favour this interpretation because it includes the effect of secular perturbations and the disc can survive for Gyr time-scales. The second model is a misaligned ring. Because there is an ambiguity in the orientation of the ring, which could be reflected in the sky plane, this ring either has near-polar orbits similar to the first model or has a 30 ° misalignment. The misaligned ring, interpreted as the result of a recent collision, is shown to be implausible from constraints on the collisional and dynamical evolution. Because disc+star systems with separations similar to 99 Herculis should form coplanar, possible formation scenarios involve either a close stellar encounter or binary exchange in the presence of circumstellar and/or circumbinary discs. Discovery and characterization of systems like 99 Herculis will help understand processes that result in planetary system misalignment around both single and multiple stars. [ABSTRACT FROM AUTHOR]

ABSTRACT The origin of interstellar dust in galaxies is poorly understood, particularly the relative contributions from supernovae and the cool stellar winds of low-intermediate-mass stars. Recently, large masses of newly formed dust have been discovered in the ejecta of core-collapse supernovae. Here, we present Herschel Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) photometry at 70-500 m of the historical, young supernova remnants: Kepler and Tycho, both thought to be the remnants of Type Ia explosion events. We detect a warm dust component in Kepler's remnant with and mass ; this is spatially coincident with thermal X-ray emission and optical knots and filaments, consistent with the warm dust originating in the circumstellar material swept up by the primary blast wave of the remnant. Similarly for Tycho's remnant, we detect warm dust at with mass . Comparing the spatial distribution of the warm dust with X-rays from the ejecta and swept-up medium, and Hα emission arising from the post-shock edge, we show that the warm dust is swept up interstellar material. We find no evidence of a cool (25-50 K) component of dust with mass ≥0.07 M⊙ as observed in core-collapse remnants of massive stars. Neither the warm or cold dust components detected here are spatially coincident with supernova ejecta material. We compare the lack of observed supernova dust with a theoretical model of dust formation in Type Ia remnants which predicts dust masses of 88(17) × 10−3 M⊙ for ejecta expanding into ambient surrounding densities of 1(5) cm−3. The model predicts that silicon- and carbon-rich dust grains will encounter, at most, the interior edge of the observed dust emission at ∼400 years, confirming that the majority of the warm dust originates from swept-up circumstellar or interstellar grains (for Kepler and Tycho, respectively). The lack of cold dust grains in the ejecta suggests that Type Ia remnants do not produce substantial quantities of iron-rich dust grains and has important consequences for the 'missing' iron mass observed in ejecta. Finally, although, we cannot completely rule out a small mass of freshly formed supernova dust, the Herschel observations confirm that significantly less dust forms in the ejecta of Type Ia supernovae than in the remnants of core-collapse explosions. [ABSTRACT FROM AUTHOR]

In 2007, R Coronae Borealis (R CrB) went into a historically deep and long decline. In this state, the dust acts like a natural coronagraph at visible wavelengths, allowing faint nebulosity around the star to be seen. Imaging has been obtained from 0.5 to 500 µm with Gemini/GMOS, Hubble Space Telescope/WFPC2, Spitzer/MIPS, and Herschel/SPIRE. Several of the structures around R CrB are cometary globules caused by wind from the star streaming past dense blobs. The estimated dust mass of the knots is consistent with their being responsible for the R CrB declines if they form along the line of sight to the star. In addition, there is a large diffuse shell extending up to 4 pc away from the star containing cool 25 K dust that is detected all the way out to 500 µm. The spectral energy distribution of R CrB can be well fitted by a 150 AU disk surrounded by a very large diffuse envelope which corresponds to the size of the observed nebulosity. The total masses of the disk and envelope are 10-4 and 2 M⊙, respectively, assuming a gas-to-dust ratio of 100. The evidence pointing toward a white dwarf merger or a final-helium-shell flash origin for R CrB is contradictory. The shell and the cometary knots are consistent with a fossil planetary nebula. Along with the fact that R CrB shows significant lithium in its atmosphere, this supports the final-helium-shell flash. However, the relatively high inferred mass of R CrB and its high fluorine abundance support a white dwarf merger. [ABSTRACT FROM AUTHOR]

Debris discs – analogous to the asteroid and Kuiper–Edgeworth belts in the Solar system – have so far mostly been identified and studied in thermal emission shortward of . The Herschel space observatory and the Submillimetre Common-User Bolometer Array-2 (SCUBA-2) camera on the James Clerk Maxwell Telescope will allow efficient photometric surveying at 70 to , which allows for the detection of cooler discs not yet discovered, and the measurement of disc masses and temperatures when combined with shorter wavelength photometry. The SCUBA-2 Unbiased Nearby Stars survey (SUNS) and the Disc Emission via a Bias-free Reconnaissance in the Infrared/Submillimetre (DEBRIS) Herschel Open Time Key Project are complementary legacy surveys observing samples of ∼500 nearby stellar systems. To maximize the legacy value of these surveys, great care has gone into the target selection process. This paper describes the target selection process and presents the target lists of these two surveys. [ABSTRACT FROM AUTHOR]

ABSTRACT The origin of interstellar dust in galaxies is poorly understood, particularly the relative contributions from supernovae and the cool stellar winds of low-intermediate-mass stars. Recently, large masses of newly formed dust have been discovered in the ejecta of core-collapse supernovae. Here, we present Herschel Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) photometry at 70-500 m of the historical, young supernova remnants: Kepler and Tycho, both thought to be the remnants of Type Ia explosion events. We detect a warm dust component in Kepler's remnant with and mass ; this is spatially coincident with thermal X-ray emission and optical knots and filaments, consistent with the warm dust originating in the circumstellar material swept up by the primary blast wave of the remnant. Similarly for Tycho's remnant, we detect warm dust at with mass . Comparing the spatial distribution of the warm dust with X-rays from the ejecta and swept-up medium, and Hα emission arising from the post-shock edge, we show that the warm dust is swept up interstellar material. We find no evidence of a cool (25-50 K) component of dust with mass ≥0.07 M⊙ as observed in core-collapse remnants of massive stars. Neither the warm or cold dust components detected here are spatially coincident with supernova ejecta material. We compare the lack of observed supernova dust with a theoretical model of dust formation in Type Ia remnants which predicts dust masses of 88(17) × 10−3 M⊙ for ejecta expanding into ambient surrounding densities of 1(5) cm−3. The model predicts that silicon- and carbon-rich dust grains will encounter, at most, the interior edge of the observed dust emission at ∼400 years, confirming that the majority of the warm dust originates from swept-up circumstellar or interstellar grains (for Kepler and Tycho, respectively). The lack of cold dust grains in the ejecta suggests that Type Ia remnants do not produce substantial quantities of iron-rich dust grains and has important consequences for the 'missing' iron mass observed in ejecta. Finally, although, we cannot completely rule out a small mass of freshly formed supernova dust, the Herschel observations confirm that significantly less dust forms in the ejecta of Type Ia supernovae than in the remnants of core-collapse explosions. [ABSTRACT FROM AUTHOR]