arXiv subjects

N. R. Deacon

Publications and source records attributed to N. R. Deacon.

At least 19 recordsLinked to original sources

arXiv2020

Wide binaries are rare in open clusters

The population statistics of binary stars are an important output of star formation models. However populations of wide binaries evolve over time due to interactions within a system's birth environment and the unfolding of wide, hierarchical triple systems. Hence the wide binary populations observed in star forming regions or OB associations may not accurately reflect the wide binary populations that will eventually reach the field. We use Gaia DR2 data to select members of three open clusters, Alpha~Per, the Pleiades and Praesepe and to flag cluster members that are likely unresolved binaries due to overluminosity or elevated astrometric noise. We then identify the resolved wide binary population in each cluster, separating it from coincident pairings of unrelated cluster members. We find that these clusters have an average wide binary fraction in the 300-3000\,AU projected separation range of 2.1$\pm^{0.4}_{0.2}$\% increasing to 3.0$\pm^{0.8}_{0.7}$\% for primaries with masses in the 0.5-1.5\,$M_{\odot}$ range. This is significantly below the observed field wide binary fraction, but shows some wide binaries survive in these dynamically highly processed environments. We compare our results with another open cluster (the Hyades) and two populations of young stars that likely originated in looser associations (Young Moving Groups and the Pisces-Eridanus stream). We find that the Hyades also has a deficit of wide binaries while the products of looser associations have wide binary fractions at or above field level.

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arXiv2019

Data-driven stellar parameters for southern TESS FGK targets

We present stellar parameter estimates for 939,457 southern FGK stars that are candidate targets for the TESS mission. Using a data-driven method similar to the CANNON, we build a model of stellar colours as a function of stellar parameters. We then use these in combination with stellar evolution models to estimate the effective temperature, gravity, metallicity, mass, radius and extinction for our selected targets. Our effective temperature estimates compare well with those from spectroscopic surveys and the addition of Gaia DR2 parallaxes allows us to identify subgiant interlopers into the TESS sample. We are able to estimate the radii of TESS targets with a typical uncertainty of 9.3\%. This catalogue can be used to screen exoplanet candidates from TESS and provides a homogeneous set of stellar parameters for statistical studies.

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arXiv2017

Identification of partially resolved binaries in Pan-STARRS1 data

Using shape measurement techniques developed for weak lensing surveys we have identified three new ultracool binaries in the Pan-STARRS1 survey. Binary companions which are not completely resolved can still alter the shapes of stellar images. These shape distortions can be measured if PSF anisotropy caused by the telescope is properly accounted for. We show using both a sample of known binary stars and simulated binaries that we can reliably recover binaries wider than around 0.3" and with flux ratios greater than around 0.1. We then applied our method to a sample of ultracool dwarfs within 30pc with 293 objects having sufficient Pan-STARRS1 data for our method. In total we recovered all but one of the 11 binaries wider than 0.3" in this sample. Our one failure was a true binary detected with a significant but erroneously high ellipticity which led it to be rejected in our analysis. We identify three new binaries, one a simultaneous discovery, with primary spectral types M6.5, L1 and T0.5. These latter two were confirmed with Keck/NIRC2 follow-up imaging. This technique will be useful for identifying large numbers of stellar and substellar binaries in the upcoming LSST and DES sky surveys.

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arXiv2017

2MASS 0213+3648 C: A wide T3 benchmark companion to an an active, old M dwarf binary

We present the discovery of a 360 AU separation T3 companion to the tight (3.1 AU) M4.5+M6.5 binary 2MASS J02132062+3648506. This companion was identified using Pan-STARRS1 data and, despite its relative proximity to the Sun (22.2$_{-4.0}^{+6.4}$ pc; Pan-STARRS1 parallax) and brightness ($J$=15.3), appears to have been missed by previous studies due to its position near a diffraction spike in 2MASS. The close M~dwarf binary has active X-ray and H$α$ emission and shows evidence for UV flares. The binary's weak {\it GALEX} UV emission and strong Na I 8200ÅNa absorption leads us to an age range of $\sim$1-10Gyr. Applying this age range to evolutionary models implies the wide companion has a mass of 0.063$\pm$0.009\,$M_{\odot}$. 2MASS J0213+3648 C provides a relatively old benchmark close to the L/T transition and acts as a key, older comparison to the much younger early-T companions HN~Peg~B and GU~Psc~b.

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arXiv2015

A Pan-STARRS1 study of the relationship between wide binarity and planet occurrence in the Kepler field

The NASA Kepler mission has revolutionised time-domain astronomy and has massively expanded the number of known extrasolar planets. However, the effect of wide multiplicity on exoplanet occurrence has not been tested with this dataset. We present a sample of 401 wide multiple systems containing at least one Kepler target star. Our method uses Pan-STARRS1 and archival data to produce an accurate proper motion catalogue of the Kepler field. Combined with Pan-STARRS1 SED fits and archival proper motions for bright stars, we use a newly developed probabilistic algorithm to identify likely wide binary pairs which are not chance associations. As by-products of this we present stellar SED templates in the Pan-STARRS1 photometric system and conversions from this system to Kepler magnitudes. We find that Kepler target stars in our binary sample with separations above 6 arcseconds are no more or less likely to be identified as confirmed or candidate planet hosts than a weighted comparison sample of Kepler targets of similar brightness and spectral type. Therefore we find no evidence that binaries with projected separations greater than 3,000AU affect the occurrence rate of planets with P<300days around FGK stars.

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arXiv2014

Pre-outburst observations of Nova Del 2013 from Pan-STARRS 1

Nova Delphini 2013 was identified on the 14th of August 2013 and eventually rose to be a naked eye object. We sought to study the behaviour of the object in the run-up to outburst and to compare it to the pre-outburst photometric characteristics of other novae. We searched the Pan-STARRS 1 datastore to identify pre-outburst photometry of Nova Del 2013 and identified twenty-four observations in the 1.2 years before outburst. The progenitor of Nova Delphini showed variability of a few tenths of a magnitude but did not brighten significantly in comparison with archival plate photometry. We also found that the object did not vary significantly on the approximately half hour timescale between pairs of Pan-STARRS 1 observations.

astro-ph.HE↗

arXiv2014

A global cloud map of the nearest known brown dwarf

Brown dwarfs -- substellar bodies more massive than planets but not massive enough to initiate the sustained hydrogen fusion that powers self-luminous stars -- are born hot and slowly cool as they age. As they cool below about 2,300 K, liquid or crystalline particles composed of calcium aluminates, silicates and iron condense into atmospheric 'dust', which disappears at still cooler temperatures (around 1,300 K). Models to explain this dust dispersal include both an abrupt sinking of the entire cloud deck into the deep, unob- servable atmosphere and breakup of the cloud into scattered patches (as seen on Jupiter and Saturn). Thus far, observations of brown dwarfs have been limited to globally integrated measurements, which can reveal surface inhomogeneities but cannot unambiguously resolve surface features. Here we report a two-dimensional map of a brown dwarf's surface that allows identification of large-scale bright and dark features, indicative of patchy clouds.

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arXiv2013

A young hierarchical triple system harbouring a candidate debris disc

We report the detection of a wide young hierarchical triple system where the primary has a candidate debris disc. The primary, TYC 5241-986-1 A, is a known Tycho star which we classify as a late-K star with emission in the X-ray, near and far-UV and Hα suggestive of youth. Its proper motion, photometric distance (65-105 pc) and radial velocity lead us to associate the system with the broadly defined Local Association of young stars but not specifically with any young moving group. The presence of weak lithium absorption and X-ray and calcium H and K emission support an age in the 20 to ~125 Myr range. The secondary is a pair of M4.5+-0.5 dwarfs with near and far UV and Hα emission separated by approximately 1 arcsec (~65-105 AU projected separation) which lie 145 arcsec (9200-15200 AU) from the primary. The primary has a WISE 22 micron excess and follow-up Herschel observations also detect an excess at 70 micron. The excess emissions are indicative of a 100-175 K debris disc. We also explore the possibility that this excess could be due to a coincident background galaxy and conclude that this is unlikely. Debris discs are extremely rare around stars older than 15 Myr, hence if the excess is caused by a disc this is an extremely novel system.

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arXiv2012

Astrometric and photometric initial mass functions from the UKIDSS Galactic Clusters Survey: III Praesepe

Over the past decades open clusters have been the subject of many studies. Such studies are crucial considering that the universality of the Initial Mass Function is still a subject of current investigations. Praesepe is an interesting open cluster for the study of the stellar and substellar mass function (MF), considering its intermediate age and its nearby distance. Here we present the results of a wide field, near-infrared study of Praesepe using the Data Release 9 (DR9) of the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey (GCS). We obtained cluster candidates of Praesepe based on a 3sigma astrometric and 5 band photometric selection. We derived a binary frequency for Praesepe of 25.6+/-3.0% in the 0.2-0.45Msol mass range, 19.6+/-3.0% for 0.1-0.2Msol, and 23.2+/-5.6% for 0.07-0.1Msol. We also studied the variability of the cluster candidates of Praesepe and we conclude that seven objects could be variable. We inferred the luminosity function of Praesepe in the Z- and J- bands and derived its MF. We observe that our determination of the MF of Praesepe differs from previous studies: while previous MFs present an increase from 0.6 to 0.1Msol, our MF shows a decrease. We looked at the MF of Praesepe in two different regions of the cluster, i.e. within and beyond 1.25deg, and we observed that both regions present a MF which decrease to lower masses. We compared our results with the Hyades, the Pleiades and alpha Per MF in the mass range of 0.072-0.6Msol and showed that the Praesepe MF is more similar to alpha Per although they are respectively aged ~85 and ~600Myr. Even though of similar age, the Praesepe remains different than the Hyades, with a decrease in the MF of only ~0.2 dex from 0.6 down to 0.1Msol, compared to ~1 dex for the Hyades.

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arXiv2012

Astrometric and photometric initial mass functions from the UKIDSS Galactic Clusters Survey: II The Alpha Persei open cluster

We present the results of a deep (J=19.1 mag) infrared (ZYJHK) survey over the full Alpha Persei open cluster extracted from the Data Release 9 of the UKIRT Infrared Deep Sky Survey Galactic Clusters Survey. We have selected ~700 cluster member candidates in ~56 square degrees in \APer{} by combining photometry in five near-infrared passbands and proper motions derived from the multiple epochs provided by the UKIDSS GCS DR9. We also provide revised membership for all previously published APer low-mass stars and brown dwarfs recovered in GCS based on the new photometry and astrometry provided by DR9. We find no evidence of $K$-band variability in members of APer with dispersion less than 0.06-0.09 mag. We employed two independent but complementary methods to derive the cluster luminosity and mass functions: a probabilistic analysis and a more standard approach consisting of stricter astrometric and photometric cuts. We find that the resulting luminosity and mass functions obtained from both methods are consistent. We find that the shape of the APer mass function is similar to that of the Pleiades although the characteristic mass may be higher after including higher mass data from earlier studies (the dispersion is comparable). We conclude that the mass functions of APer, the Pleiades, and Praesepe are best reproduced by a log-normal representation similar to the system field mass function although with some variation in the characteristic mass and dispersion values.

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arXiv2012

Astrometric and photometric mass functions of the old open cluster Praesepe from the UKIDSS GCS

Here we present the results of a wide-field (~36 sq. deg.) near-infrared (ZYJHK) survey of the Praesepe cluster using the Data Release 9 of the UKIRT Infrared Deep Sky Survey Galactic Clusters Survey. We selected cluster candidates of Praesepe based on astrometry and photometry. With our candidate list, we have obtained the luminosity function of Praesepe in the Z and J bands, and we have derived the mass function of Praesepe from 0.6 down to 0.072 Msol. Moreover, we have estimated the binarity of the Praesepe members in the 0.45-0.07 Msol mass range and as well as their variability.

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arXiv2010

Ultracool Dwarf Science from Widefield Multi-Epoch Surveys

Widefield surveys have always provided a rich hunting ground for the coolest stars and brown dwarfs. The single epoch surveys at the beginning of this century greatly expanded the parameter space for ultracool dwarfs. Here we outline the science possible from new multi-epoch surveys which add extra depth and open the time domain to study.

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arXiv2010

Forty seven new T dwarfs from the UKIDSS Large Area Survey

We report the discovery of 47 new T dwarfs in the Fourth Data Release (DR4) from the Large Area Survey (LAS) of the UKIRT Infrared Deep Sky Survey with spectral types ranging from T0 to T8.5. These bring the total sample of LAS T dwarfs to 80 as of DR4. In assigning spectral types to our objects we have identified 8 new spectrally peculiar objects, and divide 7 of them into two classes. H2O-H-early have a H2O-H index that differs with the H2O-J index by at least 2 sub-types. CH4-J-early have a CH4-J index that disagrees with the H20-J index by at least 2 subtypes. We have ruled out binarity as a sole explanation for both types of peculiarity, and suggest that they may represent hitherto unrecognised tracers of composition and/or gravity. Clear trends in z'(AB)-J and Y-J are apparent for our sample, consistent with weakening absorption in the red wing of the KI line at 0.77microns with decreasing effective temperature. We have used our sample to estimate space densities for T6-T9 dwarfs. By comparing our sample to Monte-Carlo simulations of field T dwarfs for various mass functions of the form phi(M) \propto M^-alpha, we have placed weak constraints on the form of the field mass function. Our analysis suggests that the substellar mass function is declining at lower masses, with negative values of alpha preferred. This is at odds with results for young clusters that have been generally found to have alpha > 0.

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arXiv2009

A search for southern ultracool dwarfs in young moving groups

We associate 132 low-mass ultracool dwarfs in the southern hemisphere as candidate members of five moving groups using photometric and astrometric selection techniques. Of these objects, we present high resolution spectroscopy for seven candidates and combine these with previous measurements from the literature to determine spectral types and radial velocities. We thus constrain distance and space motion spectroscopically, allowing the kinematic membership of the moving groups to be assessed. Possible membership of moving groups has allowed ages and metallicities to be constrained for these objects and evolutionary models have been used to estimate their mass. We estimate that up to ~75 of our candidate moving group members should be genuine, and discuss future work that will confirm and exploit this major new sample.

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arXiv2009

The IPHAS-POSS-I proper motion survey of the Galactic Plane

We present a proper motion survey of the Galactic plane, using IPHAS data and POSS-I Schmidt plate data as a first epoch, that probes down to proper motions below 50 milliarcseconds per year. The IPHAS survey covers the northern plane ($|b| < 5^{\circ}$) with CCD photometry in the $r$, $i$ and H$α$ passbands. We examine roughly 1400 sq. deg. of the IPHAS survey area and draw up a catalogue containing 103058 objects with significant proper motions below 150 millarcseconds per year in the magnitude range 13.5$< r' <$19. Our survey sample contains large samples of white dwarfs and subdwarfs which can be identified using a reduced proper motion diagram. We also found several objects with IPHAS colours suggesting H$α$ emission and significant proper motions. One is the known cataclysmic variable GD552; two are known DB white dwarfs and five others are found to be non-DA (DB and DC) white dwarfs, which were included in the H$α$ emission line catalogue due to their lack of absorption in the H$α$ narrow-band.

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arXiv2009

Two distant brown dwarfs in the UKIRT Infrared Deep Sky Survey Deep Extragalactic Survey Data Release 2

We present the discovery of two brown dwarfs in the UKIRT Infrared Deep Sky Survey (UKIDSS) Deep Extragalactic Survey (DXS) Data Release 2. Both objects were selected photometrically from six square degrees in DXS for their blue J-K colour and the lack of optical counterparts in the Sloan Digital Sky Survey (SDSS) Stripe 82. Additional optical photometry provided by the Canada-France-Hawaii Telescope Legacy Survey (CFHT-LS) corroborated the possible substellarity of these candidates. Subsequent methane imaging of UDXS J221611.51+003308.1 and UDXS J221903.10+002418.2, has confirmed them as T7$\pm$1 and T6$\pm$1 dwarfs at photometric distances of 81 (52-118 pc) and 60 (44-87 pc; 2 sigma confidence level). A similar search in the second data release of the Ultra Deep Survey over a smaller area (0.77 square degree) and shallower depth didn't return any late-T dwarf candidate. The numbers of late-T dwarfs in our study are broadly in line with a declining mass function when considering the current area and depth of the DXS and UDS. These brown dwarfs are the first discovered in the VIMOS 4 field and among the few T dwarfs found in pencil-beam surveys. They are valuable to investigate the scale height of T dwarfs.

astro-ph.GA↗

arXiv2008

The UKIDSS-2MASS Proper Motion Survey I: Ultracool dwarfs from UKIDSS DR4

The UKIRT Infrared Deep Sky Survey (UKIDSS) is the first of a new generation of infrared surveys. Here we combine the data from two UKIDSS components, the Large Area Survey (LAS) and the Galactic Cluster Survey (GCS), with 2MASS data to produce an infrared proper motion survey for low mass stars and brown dwarfs. In total we detect 267 low mass stars and brown dwarfs with significant proper motions. We recover all ten known single L dwarfs and the one known T dwarf above the 2MASS detection limit in our LAS survey area and identify eight additional new candidate L dwarfs. We also find one new candidate L dwarf in our GCS sample. Our sample also contains objects from eleven potential common proper motion binaries. Finally we test our proper motions and find that while the LAS objects have proper motions consistent with absolute proper motions, the GCS stars may have proper motions which are significantly under-estimated. This is due possibly to the bulk motion of some of the local astrometric reference stars used in the proper motion determination.

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arXiv2008

Fifteen new T dwarfs discovered in the UKIDSS Large Area Survey

We present the discovery of fifteen new T2.5-T7.5 dwarfs (with estimated distances between ~24-93pc, identified in the first three main data releases of the UKIRT Infrared Deep Sky Survey. This brings the total number of T dwarfs discovered in the Large Area Survey (to date) to 28. These discoveries are confirmed by near infrared spectroscopy, from which we derive spectral types on the unified scheme of Burgasser et al. (2006). Seven of the new T dwarfs have spectral types of T2.5-T4.5, five have spectral types of T5-T5.5, one is a T6.5p, and two are T7-7.5. We assess spectral morphology and colours to identify T dwarfs in our sample that may have non-typical physical properties (by comparison to solar neighbourhood populations). The colours of the full sample of LAS T dwarfs show a possible trend to bluer Y-J with decreasing effective temperature beyond T8. By accounting for the main sources of incompleteness (selection, follow-up and spatial) as well as the effects of unresolved binarity and Malmquist bias, we estimate that there are 17+-4 >=T4 dwarfs in the J<=19 volume of the LAS second data release. Comparing this to theoretical predictions is most consistent with a sub-stellar mass function exponent alpha between -1.0 and 0. This is consistent with the latest 2MASS/SDSS constraint (which is based on lower number statistics), and is significantly lower than the alpha~1.0 suggested by L dwarf field populations, possibly a result of the lower mass range probed by the T dwarf class.

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