Archive for solar neighbourhood

Local solar space: the very nearby and coolest known brown dwarf, WISE 0855-0714

Posted in astronomy with tags , on May 19, 2016 by Tim Kendall

432836_900The above image is found by google and taken courtesy of a website located in Siberia: credit: http://za-neptunie.livejournal.com/55097.html. It shows the detections of WISE 0855-0714 by the WISE and Spitzer infrared space telescopes. Each field of view is about an arcminute on a side. At top left (first red circle) the object is detected by WISE in 2010. At a third epoch (top right and third red circle) is the Spitzer detection, shown at three further epochs following (lower panels). The object is far too faint to be seen in the optical Digitized Sky Survey data. The status of this object, with such a low effective surface temperature and lying only 2.31 pc distant, makes it unique, for now. Today new Hubble photometry has been reported in arXiv marginally detecting the object at visible magnitude >26 and also giving an H-band (F160W) magnitude of 23.90±0.02. Spectroscopically, it is only possible to say it is later than Y2, and a very recent report on first spectroscopy, only possible so far in the range 4.5 – 5.2µm, shows thermal emission strikingly like Jupiter.

Advertisements

At the observational frontier of local solar space: RECONS and the ten parsec census

Posted in astronomy with tags , , on April 28, 2016 by Tim Kendall

RECONS-grabImage credit: A. Riedel and the RECONS group, P.I. Todd J. Henry taken from a new visualization by the RECONS consortium (www.recons.org) which can be seen on youtube. This is my final post (for now) on the subject of the completeness of our knowledge of stellar and planetary systems near the Sun. Stars here are plotted coloured broadly by spectral type and sized approximately by luminosity class (dwarfs or giants). The horizontal blue circle is the galactic plane crossed by the equatorial plane (grey circle) plotted at 2, 5, 10 and 25 parsecs distance. RECONS is preparing a 10 parsec census for publication and leads the field in both observation and visualization. The latest data were presented last year by Henry to the 227th meeting of the American Astronomical Society, and I reproduce the abstract in part below. In the meantime, Bihain & Scholz (2016) have investigated the projected distribution of brown dwarfs around the Sun and listed 26 brown dwarfs within 6.5 parsecs distance (as compared to 136 stars) in their Table 1 (also below):

The sample of stars, brown dwarfs, and exoplanets known within 10 parsecs of our Solar System as of January 1, 2015 is presented. All systems have trigonometric parallaxes of 100 mas or more with errors of 10 mas or less. Included in the sample are 12 systems in the southern sky added to the sample via new parallaxes from the RECONS (REsearch Consortium On Nearby Stars, www.recons.org) effort at the CTIO/SMARTS 0.9m.The census consists of 366 stars (including the Sun and white dwarfs), 37 brown dwarfs, and 34 planets (eight in our Solar System and 26 exoplanets). Red dwarfs clearly dominate the sample, accounting for 75% of all stars known within 10 pc, while brown dwarfs are currently outnumbered 10 to 1 by stars. The completeness of the sample is assessed, indicating that additional discoveries of red, brown, and white dwarfs within 10 pc, both as primaries and secondaries, are likely, although we estimate that roughly 90% of the stellar systems have been identified. The evolution of the 10 pc sample over the past 70 years is outlined to illustrate the growth of the sample. The luminosity and mass functions are described. In contrast to many studies, once all known close multiples are resolved into individual components, the true stellar mass function rises to the end of the main sequence. With far fewer brown dwarfs than stars, different formation scenarios for objects that fuse hydrogen and those that do not are likely. Of 270 stellar primaries, 28% have companion stars, only 2% have brown dwarf companions, and 6% have detected planets. The planetary rate so far is low but climbing, while searches for brown dwarf companions to stars within 10 pc have been quite rigorous, so the brown dwarf companion rate is unlikely to rise noticeably. Overall, the solar neighborhood is dominated by small stars that are potentially orbited by many small, as yet unseen, planets.

bihain-grabBrown dwarfs near the Sun. Red dwarfs like Barnard’s star are missing. The coldest known brown dwarf WISE J0855-0714 (~250K) is third on the list following Luhman 16AB, given its WISE designation in the table. WISE J0720-0846B is the mid-T companion to Scholz’s star, a 6 pc distant M9 dwarf.

Parallaxes and proper motions of 134 southern late M, L and T dwarfs

Posted in astronomy with tags , , on April 22, 2016 by Tim Kendall

groombridge1830_720x956Stars in nearby solar space exhibit large proper motions because they are moving against a background of more distant stars. All stars have their own motion through space and most stars in the solar vicinity share approximately the velocity and direction of motion of the Sun. In the case where a parallax as well as the transverse velocity are known, the knowledge of the exact distance together with the radial velocity yields the precise motion of the star relative to the Sun. The image shows the motion of the nearby star Groombridge 1830, using two images taken a year apart. The ability to determine these basic facts is especially interesting for investigating young brown dwarfs near the Sun, as  a new paper by Weinberger et al., accepted to the Astronomical Journal, elaborates:

We report trigonometric parallaxes for 134 low mass stars and brown dwarfs, of which 38 have no previously published measurement and 79 more have improved uncertainties. Our survey targeted nearby targets, so 119 are closer than 30 pc. Of the 38 stars with new parallaxes, 14 are within 20 pc and seven are likely brown dwarfs (spectral types later than L0). These parallaxes are useful for studies of kinematics, multiplicity, and spectrophotometric calibration. Two objects with new parallaxes are confirmed as young stars with membership in nearby young moving groups: LP 870-65 in AB Doradus and G 161-71 in Argus. We also report the first parallax for the planet-hosting star GJ 3470; this allows us to refine the density of its Neptune-mass planet. One T-dwarf, 2MASS J12590470-4336243, previously thought to lie within 4 pc, is found to be at 7.8 pc, and the M-type star 2MASS J01392170-3936088 joins the ranks of nearby stars as it is found to be within 10 pc. Five stars that are over-luminous and/or too red for their spectral types are identified and deserve further study as possible young stars.

In other news the location of the still putative Planet Nine has been refined to within a twenty degree area centred on RA 2h 40m and declination -15°.

New nearby high proper motion objects from the AllWISE survey

Posted in astronomy with tags , , on April 14, 2016 by Tim Kendall

Many years of work have gone into the quest to find the nearest objects outside the Solar System. The holy grail of a proper motion search based on (thermal) infrared data where low mass stars and brown dwarfs emit most of their radiation and where extinction by dust in the galactic plane is low has been achieved by the latest AllWISE survey (Kirkpatrick et al. 2016). The third nearest L dwarf was found only recently, in the galactic plane, and was fully investigated last year by Valentin Ivanov et al. The new research, led by J Davy Kirkpatrick, has found several new nearby systems of note as well as confirming a host of known objects. From the abstract:

We use the AllWISE Data Release to continue our search for WISE-detected motions. In this paper, we publish another 27,846 motion objects, bringing the total number to 48,000 when objects found during our original AllWISE motion survey are included. We use this list, along with the lists of confirmed WISE-based motion objects from the recent papers by Luhman and by Schneider et al. and candidate motion objects from the recent paper by Gagné et al. to search for widely separated, common-proper-motion systems. We identify 1,039 such candidate systems. All 48,000 objects are further analyzed using color-color and color-mag plots to provide possible characterizations prior to spectroscopic follow-up. We present spectra of 172 of these, supplemented with new spectra of 23 comparison objects from the literature, and provide classifications and physical interpretations of interesting sources. Highlights include: (1) the identification of three G/K dwarfs that can be used as standard candles to study clumpiness and grain size in nearby molecular clouds because these objects are currently moving behind the clouds, (2) the confirmation/discovery of several M, L, and T dwarfs and one white dwarf whose spectrophotometric distance estimates place them 5-20 pc from the Sun, (3) the suggestion that the Na ‘D’ line be used as a diagnostic tool for interpreting and classifying metal-poor late-M and L dwarfs, (4) the recognition of a triple system including a carbon dwarf and late-M subdwarf, for which model fits of the late-M subdwarf (giving [Fe/H] ~ -1.0) provide a measured metallicity for the carbon star, and (5) a possible 24-pc-distant K5 dwarf + peculiar red L5 system with an apparent physical separation of 0.1 pc.

Image: In this huge image of part of the southern constellation of Norma wisps of crimson gas are illuminated by rare, massive stars that have only recently ignited and are still buried deep in thick dust clouds. These scorching-hot, very young stars are only fleeting characters on the cosmic stage and their origins remain mysterious. The vast nebula where these giants were born, known as RCW 106, is captured here in fine detail by ESO’s VLT Survey Telescope (VST), at the Paranal Observatory in Chile.

Cosmography of nearby OB associations with HIPPARCOS

Posted in astronomy with tags , , on November 29, 2015 by Tim Kendall

ESO’s VLT reveals the Carina Nebula's hidden secrets(ESA press release:) Astronomers have used modern techniques to visualise data from ESA’s Hipparcos space astrometry mission in three dimensions. The treatment of the data has offered insights into the distribution of nearby stars and uncovered new groupings of stars in the solar neighbourhood, shedding light on the origins of the stars in Orion and calling into question the existence of the Gould Belt – an iconic ring-shaped structure of stars in the Milky Way. The results show the potential of 3D visualisation of the solar neighbourhood, an approach which is of particular relevance to ESA’s Gaia mission which will map the Milky Way and Local Group in 3D with unprecedented sensitivity and accuracy. The above image is the Carina Nebula, imaged using VLT/HAWK-I and roughly centred on the extremely young (~0.3 – 0.5 Myr) cluster Trumpler 14 (right), part of the Carina OB1 association. The paper is “Cosmography of OB stars in the solar neighbourhood” H. Bouy & J. Alves, 2015 A&A, 584, 13 and I reproduce in part the abstract. The must-view visualisation is here (screenshot below).ESO-Trumpler14-cluster

We construct a 3D map of the spatial density of OB stars within 500 pc from the Sun using the Hipparcos  catalogue and find three large-scale stream-like structures that allow a new view on the solar neighbourhood. The spatial coherence of these blue streams and the monotonic age sequence over hundreds of parsecs suggest that they are made of young stars, similar to the young streams that are conspicuous in nearby spiral galaxies. The three streams are 1) the Scorpius to Canis Majoris stream, covering 350 pc and 65 Myr of star formation history; 2) the Vela stream, encompassing at least 150 pc and 25 Myr of star formation history; and 3) the Orion stream, including not only the well-known Orion OB1abcd associations, but also a large previously unreported foreground stellar group lying only 200 pc from the Sun. The map also reveals a remarkable and previously unknown nearby OB association, between the Orion stream and the Taurus molecular clouds, which might be responsible for the observed structure and star formation activity in this cloud complex. This new association also appears to be the birthplace of Betelgeuse, as indicated by the proximity and velocity of the red giant. If this is confirmed, it would solve the long-standing puzzle of the origin of Betelgeuse. The well-known nearby star-forming low-mass clouds, including the nearby T and R associations Lupus, Cha, Oph, CrA, Taurus, Vela R1, and various low-mass cometary clouds in Vela and Orion, appear in this new view of the local neighbourhood to be secondary star formation episodes that most likely were triggered by the feedback from the massive stars in the streams. We also recover well-known star clusters of various ages that are currently cruising through the solar neighbourhood. Finally, we find no evidence of an elliptical structure such as the Gould belt, a structure we suggest is a 2D projection effect, and not a physical ring.Screen Shot 2015-11-28 at 10.16.01

A new T2 dwarf within 15 pc, WISE J2121-6239

Posted in astronomy with tags , on September 28, 2015 by Tim Kendall

2M2121Images: NASA/IPAC Infrared Science Archive. These near-infrared (2MASS) images clearly show the object, now identified as WISE J212100.87-623921.6. It was discovered as part of a new study of high proper motion sources from the WISE survey, published today (preprint) and accepted to MNRAS. It is interesting to note that the object is clearly defined in 2MASS with magnitudes J = 15.43, H = 14.54 and K = 14.27, ± 0.05 – 0.07 (2MASS PSC). Both because it is faint – there is no optical counterpart in the SuperCosmos catalogue, preventing a proper motion measurement over a suitably long timeline – and because T dwarfs have quite blue near-infrared colours, it was missed in the previous epoch of surveys. (Moreover, the object is in a region of the sky not observed by the Sloan Digital Sky Survey). Despite the fact that the T dwarfs populate a locus somewhat blueward of the main sequence, there is perhaps more potential for contamination by background stars than in the very red L dwarf locus, as can be seen in the figures below:jhkl1 Above: Example colour selection criteria for ultracool dwarfs in the (J-H)/(H-K) two-colour diagram: blue triangles are nearby main-sequence stars; green points ultracool M and L dwarfs; red stars are T dwarfs; deep blue circles are M subdwarfs; and purple crosses are giants. The box outlines the (J-H)/(H-K) selection limits for much redder L dwarfs. Gliese 229B is the prototypical and first to be discovered brown dwarf, with spectral type T6.

Tcomp2Above: Illustrative comparison of T dwarf JHK colours (right) compared to a selection of main sequence and other cluster, association or field dwarfs of various ages. Data for main sequence stars are from Straižys & Lazauskaitė (Baltic Astronomy, 18, 19, 2009) and are on the 2MASS system. Data for T dwarfs from S. Leggett (link here) are on the MKO system. However for these roughly comparative purposes it is sufficient to see that T dwarfs can potentially occupy the same JHK colour space as any number of background interlopers. Conversion between the two systems (and many others) are here. T dwarf data were plotted using TopCat. Note the position of WISE  J2121 and the direction of reddening.

From the preprint abstract:

The census of the solar neighborhood is almost complete for stars and becoming more complete in the brown dwarf regime. Spectroscopic, photometric and kinematic characterization of nearby objects helps us to understand the local mass function, the binary fraction, and provides new targets for sensitive planet searches. We aim to derive spectral types and spectro-photometric distances of a sample of new high proper motion sources found with the WISE satellite, and obtain parallaxes for those objects that fall within the area observed by the Vista Variables in the Via Lactea survey (VVV). We used low resolution spectroscopy and template fitting to derive spectral types, multiwavelength photometry to characterize the companion candidates and obtain photometric distances. Multi-epoch imaging from the VVV survey was used to measure the parallaxes and proper motions for three sources. We confirm a new T2 brown dwarf within 15 pc. We derived optical spectral types for twenty four sources, mostly M dwarfs within 50 pc. We addressed the wide binary nature of sixteen objects found by the WISE mission and previously known high proper motion sources. Six of these are probably members of wide binaries, two of those are new, and present evidence against the physical binary nature of two candidate binary stars found in the literature, and eight that we selected as possible binary systems.

The spectrum of the object is compared to T1, T2 and T3 spectral standards below (taken from the same paper).

WISE 2121-62 spec.

WD 1242-105: a new merging white dwarf binary in the solar neighborhood

Posted in astronomy with tags , , on March 3, 2015 by Tim Kendall

WD1242-105
Six by six arcminute field around the white dwarf WD 1242-105, courtesy SDSS DR9. The WD is the bluish object at centre. This nearby (39 pc) white dwarf has been found to be a binary object which will merge within three quarters of a billion years, but not catastrophically, i.e. it is likely not a Type Ia supernova progenitor. The paper is J.H. Debes et al., 2015, to appear in the Astronomical Journal (preprint pdf). From the abstract:

Characterizing the local space density of double degenerate binary systems is a complementary approach to broad sky surveys of double degenerates to determine the expected rates of white dwarf binary mergers, in particular those that may evolve into other observable phenomena such as extreme helium stars, Am CVn systems, and supernovae Ia. However, there have been few such systems detected in local space. We report here the discovery that WD 1242−105, a nearby bright WD, is a double-line spectroscopic binary consisting of two degenerate DA white dwarfs of similar mass and temperature, despite it previously having been spectroscopically characterized as a single degenerate. Follow-up photometry, spectroscopy, and trigonometric parallax have been obtained in an effort to determine the fundamental parameters of each component of this system. The binary has a mass ratio of 0.7 and a trigonometric parallax of 25.5 mas, placing it at a distance of 39 pc. The system’s total mass is 0.95 M⊙ and has an orbital period of 2.85 hours, making it the strongest known gravitational wave source (logh=−20.78) in the mHz regime. Because of its orbital period and total mass, WD 1242−105 is predicted to merge via gravitational radiation on a timescale of 740 Myr, which will most likely not result in a catastrophic explosion.

It is interesting to note the existence of other similar objects relatively close to the Sun, and their eventual fates. The paper authors write (some references omitted):

There are other double degenerate systems that are likely to be closer than WD 1242−105, but lack measured parallaxes or will not merge within a Hubble time. Another merging WD system with a period roughly twice as long as WD 1242−105, NLTT 53177, may be closer by a few parsecs, given the inferred spectroscopic distance of its two components. WD 1242−105 is a near twin of the compact component to the WD 1704+481 system, which consists of three white dwarfs, two of which are in an orbit with a period of 0.145 d. The mass ratio of this pair is also 0.7, with a similar difference in their gravitational redshifts. The spectroscopic distance of the distant third component is 40 pc, which is similar to WD 1242−105’s parallax. Finally, there are other double degenerate systems within 25 pc of the Sun, but those have gravitational wave merger times longer than a Hubble time. We can also investigate the eventual fate of the system. [Figure 5 shows] WD 1242−105 compared to other DDs and relative to the stability criteria of Marsh et al. (2004), which dictates whether objects merge violently with the possibility of detonation or stably through Roche lobe overflow mass transfer. All of the massive merger systems in the ELM Survey are found due to the ≈ 0.2M⊙ ELM white dwarfs. Hence, these tend to have extreme mass ratios (q ≈ 0.2), which should lead to stable mass transfer AM CVn objects. On the other hand, WD 1242−105 has q = 0.7, which will lead to unstable mass transfer and a merger.

tumblr_my0jq0AA9z1qdm6myo1_500

Record-breaking new brown dwarf: temperature 250 K, distance 2.2 pc

Posted in astronomy with tags , , , , on April 28, 2014 by Tim Kendall

1-starisdiscov

Artistic impression (above), graphic and text credits: phys.org/Penn State

(Phys.org) —A “brown dwarf” star that appears to be the coldest of its kind—as frosty as Earth’s North Pole—has been discovered by a Penn State University astronomer using NASA’s Wide-field Infrared Survey Explorer (WISE) and Spitzer Space Telescopes. Images from the space telescopes also pinpointed the object’s distance at 7.2 light-years away, making it the fourth closest system to our Sun.

“It is very exciting to discover a new neighbor of our solar system that is so close,” said Kevin Luhman, an associate professor of astronomy and astrophysics at Penn State and a researcher in the Penn State Center for Exoplanets and Habitable Worlds. “In addition, its extreme temperature should tell us a lot about the atmospheres of planets, which often have similarly cold temperatures.”

Brown dwarfs start their lives like stars, as collapsing balls of gas, but they lack the mass to burn nuclear fuel and radiate starlight. The newfound coldest brown dwarf, named WISE J085510.83-071442.5, has a chilly temperature between minus 54 and 9 degrees Fahrenheit (minus 48 to minus 13 degrees Celsius). Previous record holders for coldest brown dwarfs, also found by WISE and Spitzer, were about room temperature.

Kevin Luhman and Penn State do it again! The preprint is in arXiv today also and the paper already published in the Astrophysical Journal, vol. 786 (2014), L18. Concerning the new object, its parallax is 0.454+/-0.045 arcseconds and the mass is likely to be in the range three to ten Jupiter masses. For more on high proper motion objects in the Wide-field Infrared Survey Explorer dataset, there is another new paper in press at ApJ, Luhman & Sheppard, preprint.

starisdiscov

Update: Penn State grad student Benjamin Nelson and collaborators have solved the ongoing mystery of the inner 55 Cancri system, one of the first exoplanet systems found (1997) and itself a close neighbour to the Sun, some 12 parsecs distant. Collecting together the huge dataset, Nelson has now found a dynamically plausible system of orbital resonances. Note the three massive inner planets, all closer to 55 Cnc than Mercury is to the Sun. An accurate mass for the innermost planet e was given in 2012. The outermost planet d was found in 2002 and lies further out in the system, 5.5 AU distant from the sunlike central star.

Ford_55-Cnc-linear_4-2014

Proper motion of the two parsec distant brown dwarf binary WISE J104915.57-531906AB

Posted in astronomy with tags , , , , on May 12, 2013 by Tim Kendall

luhman-2pc

Image credit: Kevin Luhman/PENN State/Eberly College of Science

The recent discovery of this system, ranking third closest to the Sun after the planet-hosting alpha Centauri system and the red dwarf Barnard’s Star, has not been greeted with as much interest as it merits. Efforts to find the dim red and brown dwarfs close to the Sun over the whole sky including the galactic plane have had some previous successes, notably the record breaking object UGPS 0722-05, which was initially ascribed spectral type T10. The main figure is from the discovery paper and shows the progress of WISE J104915.57-531906 across the sky since being picked up on the DSS-IR plate in 1978. The final frame is the 2010 WISE data. Note that the point spread function of the WISE data is not as narrow as the near-infrared (1999) or red visible (1992) data, as would be expected with imaging in the thermal infrared. With accurate centroiding techniques this does not so much impede astrometric (positional) accuracy. Note also how bright the binary becomes at these increasingly long wavelengths, from the red visible around 8000 Angstroms (0.8 microns) through to WISE wavelengths, 3.6 microns in this case. Above, (lower right panel) significantly higher resolution i-band imaging from the 8 metre Gemini telescope reveals the binary nature of the brown dwarf system itself.

luhman-2pc
Image credit: Kevin Luhman/PENN State/Eberly College of Science
mamajek

The binarity is also apparent in this imaging from 1984 (left). The orientation is the same as for the other images, although the scale is different. The position angle very similar to that shown by the Gemini imaging. This suggests the binary has completed one orbit in the ~ 30 years since, in agreement with the initially published estimate. The primary has spectral type L8 and the secondary is likely near the L/T transition. The separation is 1.5 arcsec, or ~ 3 AU.

Update: Further characterisation of the binary has been performed by Kniazev et al., accepted to ApJ, who find a spectral type of T1.5±2 for the secondary using SALT spectroscopy.