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Transcript
T Tau! An Enigmatic
Eponym
Tracy Beck (STScI), Gail Schaefer (CHARA), G. Duchene
(Grenoble), M. Simon (SUNY Stony Brook), L. Prato (Lowell
Obs.), Andrea Ghez (UCLA)
T Tau! The Eponymous Pre-Main Sequence Star
R CrA
RU Lup
RW Aur
T Tau
R Mon
The Original 11 (Joy, 1945)
– Stars with absorption features
typical of F-G types
– Often associated with bright/dark
nebular regions
– Curious Emission Line spectra
– Highly Variable in Brightness (up
to 3+ mag)
RY Tau
S CrA
XZ Tau
UX Tau
UY Aur
UZ Tau
T Tau! An Enigmatic Eponym
• T Tau was chosen to represent the new
class of variables because it was:
– Among one of the brightest members of the
new class
– The best studied of the sample
– Showed a good range of the
absorption/emission features used to
characterize the set of stars
T Tau Prior to 1945…
• In the Beginning, there was J. R. Hind…
– In October 1852, Hind reported on the discovery of a
nebulosity ~35” from an apparently variable ~10th mag
star
– (T Tauri, of the variable star catalogs)
– After many observations of this nebula in the 1850’s,
several articles in the 1860’s noted that it was no longer
visible
Hind’s Variable Nebula (NGC 1555)
– Burnham (1890) discovered a second nebula nearby to
T Tauri, extending ~4” to the South
(Burnham’s Nebula, known today as HH 255)
T Tau… Prior to 1945
• Early literature attempts to identify variable
nebulae (difficult!)
• Hind’s nebula was of particular interest (Hind,
Struve, Burnham, Barnard, Temple…)
• Varied by an estimated 2-4+ magnitudes
• Keeler 1900:
“Hinds nebula presents an incontestable case of
nebular variability”
T Tau - Hind’s Variable Nebula
Hind’s Nebula
(POSS1 Blue
Plate; 1950’s)
T Tau - Hind’s Variable Nebula
Hind’s Nebula?
T Tau - Historical Variability?
• What causes a 45” extent nebula to
disappear?
• Why is Hind’s nebula not so variable
today?
• Could there be a link between T Tauri’s
variability and Hind’s nebula?
T Tau - Historical Variability
• Figure 5 from Lozinskii (Peremennie Zvezdi,
7, 76, 1949) (???)
T Tau - Historical Variability
Blue
Emulsion
Plates from
the Harvard
College
Observatory
Plate
Archives 1898 to
1953
(Beck &
Simon
2001)
T Tau - Historical Variability
• T Tau varied in optical brightness by
more than 3-4 magnitudes until the mid
~1920’s. Then this level of variability
just STOPPED.
• The optical continuum flux from T Tau is
still variable (e.g., Herbst et al. 1994) but not on the same scale, only by only
~+/-0.4 mag.
T Tau - Historical
Variability
• Lorre (1975) digitized Lick
Blue Emulsion Plates from
1899-1963 from the 36”
and 120” telescopes
(digital PSF subtraction)
• NGC 1555 Brightened and
stabilized considerably in
early 1930’s
Conclusion: Early
variability of T Tau and
surrounding (scattered
light) nebulosities
occurred because of
changes in obscuring
material close to the star
*
6 Dec. 1899
27 Dec. 1899
30 Oct. 1914
16 Nov. 1914
10 Feb. 1951
4 Feb. 1953
T Tau - A Whole Range of
“Firsts”
• First Confirmed Variable Nebula
• Prototypical Pre-Main Sequence Star
• Burnham’s Nebula - the 4” extent nebula to the
South of T Tau - was used to help define a new
class of Astronomical Sources known as
“Herbig-Haro Objects” (Herbig 1950)
• Beckwith et al. (1978) first detected near IR rovibrational H2 emission in YSOs in T Tau
• Brown et al. (1981) first detected UV electronic
transitions of H2 in YSOs in T Tau
• The Prototypical “IR Luminous Companion”
System…
T Tau - It’s IR Companion
Dyck, Simon &
Zuckerman
(1982) report
the detection
of an infrared
luminous
companion to
T Tau; ~0.”6
(100 AU)
South of the
optical star
“T Tau North” =
Optical Star
“T Tau South” = IR
Companion
T Tau North and South
Stapelfeldt et al.
(1998) analyzed HST
optical WFPC2 images
of T Tau, but didn’t
detect the IR
Companion to V~19.6
Mag!
Yet… T Tau S is
brighter than T Tau
N in the IR at
wavelengths
greater than ~3m
T Tau - IR Flux Variability
• T Tau N Doesn’t
vary in IR flux (to
~0.1mag)
• IR Variability of T
Tau S - Originally
detected by Ghez et
al. (1991)
• Shown here = 20
years of K & L-band
IR variability (Beck
et al. 2004)
T Tau - IR Variability
• IR Variability in K
and L-band for T
Tau S shows a
“redder-whenfaint” character
typical of
changes in
obscuration that
follow an ISM
extinction law
T Tau - Sigh…. An
Enigmatic… Triple?
• Using IR Speckle
techiniques at the W.
M. Keck Observatory,
Koresko et al. (2000)
reported that T Tau is
in fact a YSO
TRIPLE, T Tau S has
a ~0.”05 (7AU)
separation
companion!
T Tau! An Enigmatic YSO
Triple
• Yep. There it is. “T Tau Sb” is
confirmed by Duchene et al. (2002)
“T Tau
South A”
“T Tau
South B”
T Tau - Reconciling IR and
Radio Data?
• The Measured IR and Radio positions
of T Tau S (unresolved) from 1980
onwards have never agreed entirely
• Loinard et al. (2003), Johnson et al.
(2003) - the detected Radio flux comes
exclusively from T Tau Sb & This
provides a way to trace the orbit of T
Tau Sb back through the radio data!
T Tau! A Privileged View of a
Stellar Ejection?
• Stellar Ejection
Event?
• Radio data had
no reference
position for T Tau
Sa, assumed it’s
location was
static!
Figure 3 from Loinard et al. (2003)
T Tau - IR vs. Radio
Positions?
• Dashed line =
average IR
position of T Tau S
• Points =
Measured Radio
Positions
• (IR = Sa, Radio =
Sb)
T Tau Sb - (I’d like to Get Rid of
Sb…) but there’s NO Ejection!
• Radio data referenced to
the moving IR position of
T Tau S shows NO
evidence for an ejection
event!
• Perhaps more
importantly, IR and radio
positions for T Tau Sb
don’t coincide for data
from 2001 (differ by
~40mas)
T Tau - The Nature of the YSO
Triple Stars
T Tau N, the
Optical star, is an
actively accreting
YSO with IR disk
excess, low Av,
and a stellar type
of ~K0.
AO-fed IR
spectroscopy
shows that
T Tau Sb is a young spectral type ~M0 star with IR excess
emission, seen through about ~8mag of Av (Duchene et al.
2002)
T Tau Sa - What the…?
• Orbital
analysis of the
T Tau
system…
• BOTH stars
referenced to
the position of
T Tau N
• Schaefer et al.
(2006)
T Tau Sa - What the…?
• Schaefer et al.
(2006)
• Analyzed 10,000
possible orbital
solutions for the
Sa-Sb system
and derive a
distribution of
possible masses
• Mean Mass =
4.13 +1.58/-0.97
T Tau Sa
• T Tau Sa - A ~3 Solar mass star
• Though it is optically invisible, T Tau Sa is
the most massive star in the T Tau system!
• It is ~50% more massive than T Tau N
(one of the brightest & most massive
YSOs in Taurus!)
• How can this be?
T Tau - A look at Circumstellar
Material in the System
Akeson, Jensen & Koerner
(1998) found 3mm continuum
emission - typical of cold dust
in YSO disks - toward T Tau N,
only!
(limiting detection for T Tau S
~9mJy)
Work by Akeson et al. (2002;
2005), Eisloffel et al. (1988);
Herbst et al. (1986) all suggest
that T Tau N is viewed pole-on,
& with a disk that is viewed
nearly face-on
Amorphous
silicates, young,
embedded
YSOs
Circumstellar Disks in the
Infrared…
• To better understand T
Tau, a reminder of the
“evolution” of disk
diagnostics in the IR
• Evans et al. (2003) Spitzer Legacy - “From
Molecular Cores to
Planet Forming Disks”
• (Kessler et al. 2005;
Furlan et al. 2006)
Crystalline silicates, evolved
disks, grain growth
T Tau - Mid Infrared Silicates
from YSO Disks
• 10m
spectra
• silicates in
emission
in T Tau N,
but
Absorption
in T Tau S
T Tau! Emission/Absorption
from Silicates
• Continuum
removed
• T Tau N shows
emission only,
with structure
caused by silicate
processing and
crystalline
components
(enstatite 10.2,
forsterite 11.3m)
• T Tau S mostly
amorphous
silicate
absorption
T Tau! 10m Spectroscopy
• Skemer et
al. (2008)
showed that
the 10m
silicate
absorption
may arise
from T Tau
Sa, only!
A Quick Summary…
• T Tau N - A K0 spectral type YSO with low Av,
a circumstellar disk viewed virtually face-on,
and silicates in emission
• T Tau Sb - A ~M0 star seen through an Av of
~8mag with no firm evidence for silicates
• T Tau Sa - a ~3 Msolar YSO, obscured by ??
(presumably 8 or more) mag of Av, with
strong silicates in absorption
T Tau - Disk Inclination
Effects?
• Chiang & Goldreich (1997; 1999) passive disk
models with inclination effects:
– Superheated surface layers of inner YSO disks can
give rise to silicates in emission, if viewed face-on.
– YSOs with disks viewed edge-on will have dust
features in absorption
– Inclination effects can, however, account for only a
factor of ~2 difference in mm wavelength dust
emission (remember, T Tau N’s 3mm dust was ~6x
brighter than the null detection from T Tau S).
T Tau - Disk Inclination
Effects?
T Tau! Perpendicular Disks?
• Arguably the best studied example of noncoplanar disk material in a YSO multiple system
• Not just silicates, but also:
–
–
–
–
IR spectra and SEDs (Duchene et al. 2005)
3m Water Ice absorption (Beck et al. 2004)
H2 emission morphologies (Brown et al. in prep)
YSO Outflow morphologies - two perpendicular
outflows, 3 known HH objects associated with T
Tau (Solf & Bohm et al. 1999; … outflows Robberto et al. 1995)
T Tau! System Geometry
T Tau N, disk
viewed face-on
T Tau S,
obscured by a
circumbinary
distribution of
material
Sa/Sb each have
their own
(truncated)
disks
(Historical variability
caused by orbital
motion of T Tau S
w/r/t N?)
T Tau! Perhaps Best Studied,
but NOT Unique!
• The IR Luminous Companion Phenomenon:
– Zinnecker & Wilking (1992) first postulated that
10-15% of all YSOs have “IR Luminous
Companions”
– Optically undetected or faint, highly variable in
flux, likely more massive than their optical
primaries (Koresko et al. 1997)
T Tau (prototype)
Haro 6-10
UY Aur
XZ Tau
V773 Tau
Z CMa
WSB 4
DoAr 24E
Glass I
VW Cha
SZ 77
VV CrA
The IR Luminous Companion
Phenomenon
• Dynamical Evolution in YSO High
Order Multiples
– In an attempt to model the observed
characteristics of T Tau Sa & Sb, Reipurth
(2000) proposed that the IR Luminous
Companions are a result of dynamical
evolution in high order multiples
– Vast differences in Obscuration arise from
geometries where system components are
presently viewed through remnant material
(e.g. circum-system disks)
– Alternative interpretation to purely
“Perpendicular Disks”, but both invoke
dynamical evolution
Mis-aligned Disks in YSO
Multiples?
• Jensen et al. (2004) - Polarimetry
measurements of disk alignment in YSO
binaries and higher order multiples
– 8 YSO binaries have significant deviations from
coplanarity (though orientations differ by <30o)
– 5 o 5 YSO triples or higher order multiples show
disk alignment that deviates at a higher level
from coplanarity - disks are misaligned to
>120deg between some components
(Formation Mechanism vs. Dynamical Evolution?)
Evidence for Dynamical
Evolution in YSO Multiples
PDS 144 - Perrin et al. (2006)
HK Tau - Stapelfeldt
et al. 1998)
Mis-Aligned disks in YSO multiples could be
quite common
T Tau! An Enigmatic - but
perhaps not Atypical - Eponym
• Evolution of our knowledge of this prototypical YSO was
presented dating to the very early days of modern astronomy
• T Tau and its surrounding nebulosities varied in optical light prior
to the early ~1930’s, but this ceased abruptly
• T Tau is a YSO triple system, with two of the system components
obscured to optical invisibility, viewed through extensive
circumstellar material
• One of the optically invisible components, T Tau Sa, is a ~3 solar
mass YSO (bordering on Herbig Ae-Be star territory!)
• T Tau N has low Av, with a circumstellar disk viewed nearly faceon. It shows silicates in emission, with evidence for dust
processing
• Dynamical Evolution could explain the observed characteristics
of T Tau, and may be a common phenomenon in high order YSO
multiples