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SCUBA observations of dust around Lindroos stars: evidence for a substantial submillimetre disc population
We have observed 22 young stars from the Lindroos sample at 850 μmwith SCUBA on the James Clerk Maxwell Telescope to search for evidenceof dust discs. Stars in this sample are the less massive companions ofB-type primaries and have well-defined ages that are 10- 170 Myr; i.e.they are about to, or have recently arrived on the main sequence. Dustwas detected around three of these stars (HD 112412, 74067 and 99803B).The emission around HD 74067 is centrally peaked and is approximatelysymmetrically distributed out to ~70 arcsec from the star. This emissionarises from either a two-component disc, one circumstellar and the othercircumbinary with dust masses of 0.3 and <27 M⊕,respectively, or an unrelated background object. The other twodetections we attribute to circumsecondary discs with masses of 0.04 and0.3 M⊕. We were also able to show that a circumprimarydisc is present around HD 112413 with a similar mass to that around thecompanion HD 112412. Cross-correlation of our sample with the IRAScatalogues only showed evidence for dust emission at 25 and 60 μmtoward one star (HD 1438); none of the submillimetre detections wereevident in the far-infrared data implying that these discs are cold(>40 K assuming β= 1). Our submillimetre detections are some ofthe first of dust discs surrounding evolved stars that were not detectedby IRAS or ISO and imply that 9-14 per cent of stars could harbourpreviously undetected dust discs that await discovery in unbiased sub-mmsurveys. If these discs are protoplanetary remnants, rather thansecondary debris discs, dust lifetime arguments show that they must bedevoid of small <0.1 mm grains. Thus it may be possible to determinethe origin of these discs from their spectral energy distributions. Thelow inferred dust masses for this sample support the picture thatprotoplanetary dust discs are depleted to the levels of the brightestdebris discs (~1 M⊕) within 10 Myr, although if theextended emission of HD 74067 is associated with the star, this wouldindicate that >10 M⊕ of circumbinary material canpersist until ~60 Myr and would also support the theory that T Tauridiscs in binary systems are replenished by circumbinary envelopes.
| A study of visual double stars with early type primaries. IV Astrophysical data
Astrophysical parameters (MK class, color excess, absolute magnitude,distance, effective temperature, mass, and age) are derived fromcalibrations of the uvby-beta indices for the members of 253 doublestars with O or B type primaries and faint secondaries. The photometricspectral classification is compared to the MK classes, and the agreementis very good. The derived data together with spectroscopic and JHKL dataare used for deciding which pairs are likely to be physical and whichare optical, and it is shown that 98 (34 percent) of the secondaries arelikely to be members of physical systems. For 90 percent of the physicalpairs the projected separation between the components is less than25,000 AU. A majority of the physical secondaries are late-type stars,and 50 percent of them are contracting towards the zero-agemain-sequence. Also presented are new uvby-beta data for 43 secondariesand a computer program for determining astrophysical parameters fromuvby-beta data.
| UBVRI photometry of stars in Trapezium type systems.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977RMxAA...3..133W&db_key=AST
| The kinematics of trapezium systems.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974RMxAA...1..101A&db_key=AST
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| Сазвежђа: | Мали пас |
| Ректацензија: | 07h47m02.67s |
| Deклинација: | +00°01'23.3" |
| Apparent магнитуда: | 9.359 |
| Proper motion RA: | -0.3 |
| Proper motion Dec: | -4.5 |
| B-T magnitude: | 9.436 |
| V-T magnitude: | 9.366 |
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