Download The accretion properties of the intermediate mass Herbig Ae/Be stars

School of Physics and Astronomy
FACULTY OF MATHEMATICS AND PHYSICAL SCIENCES
Accretion properties of the intermediate mass
Herbig Ae/Be pre-main sequence stars
René Oudmaijer
(Leeds, UK)
John Fairlamb, Karim Ababakr,
Ignacio Mendigutia (Leeds), Mario
van den Ancker (ESO), John Ilee
(Cambridge)
Low mass star
formation fairly well
understood.
How does matter
accrete onto more
massive stars?
Van Boekel+ 2004
Pre-main sequence stars
•  T Tauri stars : solar mass,
magnetically controlled
accretion, veiling, optically
visible
•  Herbig Ae/Be stars :
intermediate mass, accretion
by infall, optically visible
•  Massive Young Stellar
Objects : massive, rare,
elusive, obscured (Leeds RMS)
Fairlamb+ 2015
Pre-main sequence stars
T Tauri and Herbig Ae/Be stars surrounded by disks
•  Herbig stars cover the mass range in which a transition from
magnetically controlled accretion onto star to as yet unknown
accretion onto star occurs.
•  Bridge the gap between low and high mass stars
(Monnier+ 2005)
Herbig Ae/Be stars
Some of the hottest objects are massive in their own right, and
good proxy for Massive Young Stellar Objects.
e.g. PDS 27 and PDS 37 appear in the Red MSX Source survey
Lumsden+ 2013; Ababakr+ 2015
Herbig Ae/Be stars
Some of the hottest objects are massive in their own right, and
good proxy for Massive Young Stellar Objects.
FromPDS
spectropolarimetry:
e.g.
27 and PDS 37 appear in the Red MSX Source survey
Lumsden+ 2013;
Ababakr+
2015 - see also poster by Karim Ababakr
Surrounded
by small
scale disks
Herbig Ae/Be stars even host planets
HD 100546 : Thayne Currie+ 2015 – see also poster by Mendigutia
Investigate accretion properties
across mass range
•  Obtained X-Shooter data of a large
sample of 90 Herbig Ae/Be stars –
almost all known
•  Spectra cover optical – near-infrared
wavelength range (400nm –
2.4micron) in one shot
•  Determined stellar parameters in
homogeneous manner for all objects
•  Worked out accretion rate.
•  Fairlamb+ 2015
A large sample: accretion rates
Only “direct” measure: Balmer excess: continuum emission due to
accretion shock
Determine stellar parameters, spectral type, temperature, gravity,
reddening
A large sample: accretion rates
Only “direct” measure:
Balmer excess: continuum
emission due to accretion
shock
Ø  Determine UV excess
Ø  Magnetospheric
accretion model:
accretion luminosity
Ø  Stellar radius and mass:
accretion rate
Ø  Cf. Calvet & Gullbring 1998 (T
Tauri) Muzerolle+2004, Donehew
& Brittain 2011 (Herbig)
Accretion rates
Excess – accretion
rate relationship
depends on spectral
type
Same accretion
luminosity results in
smaller relative
excess for hotter,
UV bright, B stars.
Cf. Mendigutia+ 2011
Accretion luminosity correlates with
stellar luminosity
Trend over
many orders of
magnitude
T Tauri: Natta+ 2006
Emission line luminosities correlate with both
stellar luminosity and accretion luminosity
Emission line luminosities
correlate with accretion
luminosity.
Can be used as accretion
diagnostic
Lacc determination much
easier than using UV
excess
Extended the number of
calibrated lines to entire XShooter spectral range
Fairlamb+ 2016, subm.
Mendigutia+2011, Garcia-Lopez+
2005, Muzerolle+2004, Donehew
& Brittain 2011
Accretion rate decreases with age
Accretion rate correlates with mass
But: different slope Ae and Be
objects
Occurs at similar mass as other
such findings Vink+ 2002 (see also
Muzerolle+ 2004, Grady+ 2010,
Oudmaijer+ 2011, Alecian+ 2013,
Cauley & Johns-Krull 2015)
Also, some early B-types have UV
excesses that can not be
reproduced with magnetospheric
accretion
Need another mechanism.
Boundary layer accretion instead?
Mendigutia+ in prep; Fairlamb+ 2015
MYSOs follow trend
Pomohaci+ 2016 in prep; Cooper+ 2013
Conspiracy? Lines do not trace
accretion but wind for high mass objects
Herbig Ae/Be stars as link between low and high
mass stars:
Massive Stars
could form in
clusters.
(Testi+ 1997)
Stars could form in clusters: (Testi+ 1999)
Aim is to find more about the intermediate mass stars – no
follow-on studies since 1999
Need more and better defined Herbig Stars
Find and characterize clusters around them
GAIA satellite will provide fundamental information on
a billion of stars – a factor of 10,000-100,000 better than
previous satellite HIPPARCOS which flew early 90s
Conclusions
§  Herbig Ae/Be stars bridge the gap between low and high mass
young stars and cover the mass where transition in accretion
mode occurs.
§  Conducted largest spectral survey – 0.4 – 2.4 micron spectra of
90 objects
§  Determined spectral types, temperatures, radii, reddening in
a homogeneous manner
§  Determined accretion rates “directly” from UV excess
§  Herbig Ae similar to T Tauri stars
§  Appears to be a change in accretion mode at around 3 solar
masses (mid B-type)
§  Presented relations to allow accretion rates to be determined
from line luminosities instead. Large spectral range.
Future work
GAIA – cluster work – 3D picture of clusters, age determinations
Line profile correlations provide information on accretion process
CO emission at 2.3 micron (Ilee+2014)