Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches...
-
Upload
amberlynn-barber -
Category
Documents
-
view
220 -
download
0
Transcript of Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches...
![Page 1: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/1.jpg)
Improving our knowledge on nearby stars and brown dwarfs
Ralf-Dieter ScholzAstrophysikalisches Institut Potsdam
Thüringer Landessternwarte Tautenburg, December 13, 2005
![Page 2: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/2.jpg)
•A neighbourhood of dwarfs
•Our ignorance of
neighbours
•Distances and proper
motions
•Using old
catalogues/archives
•Spectroscopic distances
•Visitors from the halo
•Finding the coolest
neighbours
![Page 3: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/3.jpg)
Proxima Centauri – the next neighbour (?)
Red dwarf, spectral type: M5, distance: 1.3 pc
Three different epoch images (SuperCOSMOS Sky Surveys = SSS):
1976 1982 1993
blue (Bj) extremely red (I) red (R)
Image size: 2 arcmin by 2 arcminProper motion: 3.9 arcsec/yr (among TOP 20 of fastest stars in
the sky)
![Page 4: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/4.jpg)
The Solar neighbourhood (www.anzwers.org/free/universe/)
![Page 5: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/5.jpg)
Stars with accurate
(trigonometric) distances
HRD-CMD forabout 22000 stars measured by the
Hipparcos satellite+
about 1000 stars with ground-based
parallaxes
most red (and white ?) dwarfs not
yet included !
www.anzwers.org/free/universe/
![Page 6: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/6.jpg)
The missing stellar neighbours5pc sample:44 systems (complete)Henry et al. (1997)
10pc sample:229 known,130 missing (36%)Henry et al. (1997)
25pc sample:~2000 known systems~3500 missing systems (63%)Henry et al. (2002)
Assumptions:1) constant space density2) complete counts within 5pc
?
?
![Page 7: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/7.jpg)
The missing stellar neighbours5pc sample:44 systems (complete)Henry et al. (1997)but: 3 new systems discovered since then!!
10pc sample:229 known,130 missing (36%)Henry et al. (1997)
25pc sample:~2000 known systems~3500 missing systems (63%)Henry et al. (2002)
Assumptions:1) constant space density2) complete counts within 5pc
?
?
![Page 8: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/8.jpg)
Why care about neighbours?
● nearest representatives of a given class of stars can be studied down to the smallest detail
● many search methods for extra-solar planets work only with nearby stars
● new classes of low-luminosity objects (late M, L, T, Y? dwarfs/subdwarfs + cool white dwarfs) are still being discovered – best chances to find them nearby
● complete picture of stellar/substellar luminosity functions, binary/multiple systems statistics, velocity distributions, etc. of different populations in a galaxy – only possible in Solar neighbourhood
![Page 9: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/9.jpg)
Proper motion as rough distance measure
● Proper motion µ = apparent motion on the sky (large values range from ~0.1 to ~10 arcsec/yr)
● Real velocity [in km/s] can only be estimated if the distance from the Sun d [in pc] is known: vtan = 4.76 · µ · d
● Typical relative velocity of local Galactic disk stars ~ 40 km/s
● Disk star with µ = 1 arcsec/yr lies typically at d ~ 10 pc
● Halo stars do not take part in Galactic rotation (~220 km/s at the location of the Sun) same µ indicates 5 times larger distance
![Page 10: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/10.jpg)
Proper motion samples are halo biased
Galactic space velocities UVW for proper motion stars from Lepine, Shara & Rich (2003):
Dotted and dashed ellipses - 2σ velocity dispersions of local disk and halo stars, respectively (Chiba & Beers 2000)Solid circles - limit for stars gravitationally bound to the Galaxy (model of Dauphole & Colins 1999)
Normal red dwarfs red subdwarfs
![Page 11: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/11.jpg)
Search tools for nearby red dwarfs
Discovery of an M6dwarf (LHS 2090) at spectroscopic distance of only 6 pc
Scholz, Meusinger & Jahreiß (2001)
Old catalogues (e.g. + new deeper and/or near-infraredLuyten Half Second sky surveys (e.g. Two Micron= LHS) und Archives All Sky Survey = 2MASS)
Proper motion + extremely red colour
![Page 12: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/12.jpg)
Continuing search among known pm stars
322 red candidates from NLTT (Scholz, Meusinger & Jahreiß 2005)
![Page 13: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/13.jpg)
How did we select them?● observable from Calar Alto (delta > -30 deg)● proper motion stars from the New Luyten Two Tenths
(NLTT) catalogue (µ > 0.18 arcsec/yr)● faint + red (optical or optical-to-NIR) objects (90%)
red giants are excluded
● + Luyten Half Second (LHS) stars (pm > 0.5 arcsec/yr) lacking spectroscopy or bibliography in SIMBAD (10%)
Problem: poor NLTT positions and photometrySolution: NLTT cross-Id. with 2MASS (2nd incremental data release), SSS+USNO A2.0, CMC, Tycho-2
![Page 14: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/14.jpg)
Preliminary photometric distance estimates
a)SSS or USNO A2.0 R magnitudes combined with 2MASS Ks:
absolute Ks vs. R-Ks relation obtained from objects with known trigonometric parallaxes (Figure)
targets selected withd < 30 pc
______________________________________________________________b) V magnitudes from CMC, Tycho-2 or other sources available: according to absolute V vs. V-Ks relation of Reid & Cruz (2002) targets selected with d < 25 pc
(Scholz, Meusinger & Jahreiß 2005)
![Page 15: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/15.jpg)
Low-resolution spectra: 2.2m@Calar Alto(Scholz, Meusinger & Jahreiß
2005)
![Page 16: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/16.jpg)
Some statistics for our sample(Scholz, Meusinger & Jahreiß 2005)
H = Hipparcos, Y = Yale parallax catalogue1..4 = distances from Reid & collaborators
![Page 17: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/17.jpg)
Comparison with other spectroscopy
R03 - Reid et al. (2003b)C02 - Cruz & Reid (2002)G00 - Gizis (2000)H96 - Hawley, Gizis & Reid (1996)K95 - Kirkpatrick, Henry & Simons (1995)
FBS - Gigoyan, Hambaryan & Azzopardi (1998)HIC - Turon et al. (1993)PPM - Röser & Bastian (1988)B98 - Buscombe (1998)L84 - Lee (1984)T00 - Torres et al. (2000)T94 - Tokovinin (1994)L98 - Li & Hu (1998)
![Page 18: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/18.jpg)
Absolute magnitude/spectral type calibration
based on data from the CNS4 (Jahreiß, in prep.)
![Page 19: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/19.jpg)
Two white dwarfs (Scholz, Meusinger & Jahreiß 2005)
LHS 1200: Teff~13000K, d=110±20pc, (U,V,W)=(-116,-184,-219)km/s, halo objectLHS 2288: Teff~4000K, d=44±7pc, vtan=140km/s, thick disk object
![Page 20: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/20.jpg)
Subdwarfs (candidates) with large velocities • - our
estimates (K and M dwarfs)
+ - objects with much smaller trigonometric parallaxes (obviously sub-dwarfs)
x - white dwarfs
∘ - assumed sub-dwarfs (values reduced by 50%)
5% of our targets are at d>50pc, 11 objects with 250<vtan<1200 km/s are assumed to be in fact subdwarfs, if so, their distances and vtan would be reduced by ~50%(we can not distinguish normal K/M dwarfs and subdwarfs based on our spectra)
(Scholz, Meusinger & Jahreiß 2005)
![Page 21: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/21.jpg)
Results of our search among NLTT stars
● 85% of our K and M dwarfs are within 30pc (72% within 25pc) high success rate! (purely photometric study with meanwhile completed 2MASS may be worth doing)
● 50 objects have spectroscopic distances d<15pc, 8 are within 10pc (three of the latter had no previous spectral types)
● Our spectroscopic distances are generally in good agreement with previous estimates based on higher resolution spectra
● Compared to expected number of missing stars in 25pc sample our study investigated/uncovered only a small fraction of them further work is needed
● The relatively hot (~DA3.5) white dwarf LHS1200 as well as 11 red (sub)dwarfs (which were selected mainly based on their proper motion) have very large space velocities typical of the Galactic halo
● There are no other brown dwarfs in Luyten’s NLTT catalogue except the M9.5 dwarf LP 944-20 deeper high pm searches are needed!
![Page 22: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/22.jpg)
How brown dwarfs differ from stars?
(www.astron.berkeley.edu/~stars/bdwarfs/)
Mass in Solar units: 1 0.6...0.08 0.08...0.013 0.001
Failed to accumulate critical mass of stars (~0.08 Msolar) during formation no hydrogen burning in their cores
Low luminosity + red colour (low surface temperature), methane, lithium, ... absorption in their spectra,mass not measurable in most cases!
![Page 23: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/23.jpg)
Spectra of late spectral types (red and brown
dwarfs)
Kirkpatrick et al. (1999)
New spectral classes L and T defined only very recently
Objects with ~2000...<1000 K surface temperature, i.e. even cooler than the coolest M dwarfs
Few late-M, 50% of early-L and all late-L and T dwarfs in the Solar neighbourhood are brown dwarfs
![Page 24: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/24.jpg)
Discovery of a bright L dwarf (Scholz & Meusinger 2002)
Detected in SSS high pm survey; spectroscopic classification with 2.2m@Calar Alto;More high pm L dwarfs classified with ESO 3.6m and NTT (Lodieu et al. 2002, 2005)
SSSPM J0829-1309:About 1 mag brighter than Kelu 1Estimated distance: 12 pc
![Page 25: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/25.jpg)
A visitor from the Galactic halo:
SSSPM J1444−2019 Extremely large proper motion: 3.5 arcsec/yr
sdM9, but L-type spectral features (RbI, FeH, CrH, no VO!)
1976
1985
1994 (Scholz, Lodieu & McCaughrean 2004)
![Page 26: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/26.jpg)
Subdwarf classification by spectral indices
Lower temperature
Lower metallicity
(Reid et al. 1995, Gizis 1997)
Lepine et al. (2003), Scholz et al. (2004)
![Page 27: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/27.jpg)
SSSPM J1444-2019: a sub-stellar subdwarf?
VLT/FORS2 spectra: Lithium not detected (Scholz, Lodieu & McCaughrean 2004)
![Page 28: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/28.jpg)
Metallicity of the coolest subdwarfs
Scholz, Lodieu & McCaughrean (2004)
![Page 29: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/29.jpg)
Statistics on all known L and T dwarfs
476 objects as of Nov. 28, 2005 in spider.ipac.caltech.edu/staff/davy/ARCHIVE/
![Page 30: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/30.jpg)
The (sub-)stellar luminosity function
Courtesy of Peter Allen
M
L
TY?
Cruz (2005)
![Page 31: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/31.jpg)
Discovery of the nearest brown
dwarf
Scholz et al. (2003)
as result of SSS high proper motion search
![Page 32: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/32.jpg)
Discovery of the nearest brown
dwarf
Scholz et al. (2003) pm + parallax + orbital motion (simulation)
... resolved as a T1+T6
binary
McCaughrean et al. (2004)
as result of SSS high proper motion search using adaptive optics at VLT+NACO
0.7 arcsec
![Page 33: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/33.jpg)
Search for cooler, Y-type brown dwarfs
New deep near-infrared survey
Pinfield et al. (2005)
![Page 34: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/34.jpg)
Search for coolest Y dwarfs near the Sun
High proper motion survey using SDSS
pm of late-L dwarf (Finkbeiner et al. 2003)
SDSS positional accuracy (Pier et al. 2004)
SDSS multi-epoch (5 years) imaging data (Ivezic 2003) can be used for pm search!
![Page 35: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/35.jpg)
Search for coolest Y dwarfs near the Sun
High proper motion survey using SDSS
pm of late-L dwarf (Finkbeiner et al. 2003)
SDSS positional accuracy (Pier et al. 2004)
SDSS multi-epoch (5 years) imaging data (Ivezic 2003) can be used for pm search!
Corresponding SDSS project just started at AIP (Scholz et al.)
![Page 36: Improving our knowledge on nearby stars and brown dwarfs Ralf-Dieter Scholz Astrophysikalisches Institut Potsdam Thüringer Landessternwarte Tautenburg,](https://reader035.fdocuments.us/reader035/viewer/2022062314/56649ea25503460f94ba5880/html5/thumbnails/36.jpg)
+Ba, Bb
Are we surrounded by as many brown dwarfs as stars?
>90% unknown!