Transcript PPV_hd169142

1. HD 169142
B-V
0.26
Type
A5Ve (Dunkin et al. 1997)
E(B-V) 0.10
Vsin i 55± 2 (Dunkin et al. 1997)
Age
4-15 Myr (van Boekel et al.
2005)
A7Ve (this study)
<0.04
Veq=244 km/s (this
study)
8 ±4 Myr (this study)
2. The Environment
The Disk and Environment
of HD 169142
C.A. Grady (Eureka Scientific and GSFC), G. Schneider (U. of Arizona),
G. Williger (JHU and U. Louisville), B. Woodgate (NASA’s GSFC),
M. Silverstone (U. of Arizona) and the HST-GO-10177 Team
The Disk of HD 169142 A:
5. The Inner Disk
While neither the NICMOS data nor the earlier data of
Kuhn et al. (2001) sample r≤0.3" without saturation,
more recent work by Habart et al. (2005) resolves the
mid-IR PAH emission. The extent of the PAH
emission is similar to HD 100546, where an eccentric
cavity is marginally resolved in fluorescent H2 (Grady
et al. 2005). Both PAH and H2 emission require direct
illumination by the star.
The r-3 radial surface brightness profile for HD 169142
is consistent with grain growth and settling in the disk
(Dullemond & Dominik 2004), resulting in a
comparatively flat disk which can only be directly
illuminated if there is a deficit of material in the inner
disk. The low NIR excess, absence of emission from
small, warm silicate grains (van Boekel et al. 2005;
Meeus et al. 2001; Sylvester et al. 1996). the absence
of [O I] emission (Acke et al. 2005), and the 3.3 mm
PAH profile (Habart & Natta 2005) all suggest a
deficit of material at r ≤20 AU relative to other, faceon Herbig Ae disks.
Fig. 1: Despite a wealth of stars in the field of HD 169142 (left)
, only 3 objects have net H emission (right), including the
Herbig Ae star, a star at the bottom of the field and 2MASS
18242929-2946559, which lies 8” SW of HD 169142. Data
obtained with the Goddard Fabry-Perot at the Apache Point
Observatory 3.5m.
Fig. 5:NICMOS camera 2 (FOV = 19.2” x 19.3”, scale: ~ 75.8 mas/pixel) direct and coronagraphic imagery of HD
169142A and its nearby environment was obtained in a single HST orbit on 2005 April 30. Each observation set
consisted of (a) two short F171M (1.71 mm) target acquisition images, (b) three deep F110W (1.1 mm) coronagraphic
images (with the target obscured by the r = 0.3” coronagraphic hole [red circles in 7”x7” fields above]), and (c) two
shallow direct (unocculted) F110W images. The spacecraft orientation was changed by 29.9° between the observation
sets to permit discriminating against roll-invariant imaging artifacts. After subtracting a suite of appropriately scaled and
registered PSF template star observations (spectral types A0-A8; J-H ± 0.3 of HD 169142A), non-instrumentally
scattered circumstellar light is seen in all PSF subtracted images where the underlying PSF structure is well matched to
the HD 169142A observations.
Fig. 2: 2MASS 18242929-2946559 is revealed as an M2.5Ve
star in Dual Imaging Spectrograph data from APO.
Fig. 3: 2MASS 18242929-2946559
is resolved into at least 2 sources
separated by 0.11” in both NICMOS
observations (right).
The circumstellar light presents as an azimuthally-symmetric region which can be traced to (at least) ~ 1.3”. The PSFsubtracted images at both field orientations are consistent with a face-on viewing geometry as originally suggested by
Dunkin et al. (1997) and found by Kuhn et al. (2001) with simultaneous dual beam polarimetric imaging in H-band. As
a null test, paired subtractions of the template PSF stars from each other were found to closely match expectations of
PSF-PSF images (Schneider et al, 2001) with small color and “breathing” (PSF stability) variations .
Fig. 6, 7: The azimuthally-medianed data for both visits
can be fit by single power laws. However, we consider
the fit for the first visit more robust as the HST PSF was
more stable and better matched to our reference PSFs.
From those data, we find a peak surface brightness at r =
0.57" of 0.5 mJy/arcsec2, with the disk surface brightness
declining by r-3. This is a comparatively steep radial
surface brightness power law, only slightly less steep
than for  Pic, and comparable to that of HD 100546
(Grady et al. 2001; Augereau et al. 2001). The disk is
intermediate in brightness between HD 141569 A or TW
Hya and faint disks like HD 163296 (Grady et al.2000).
3. System Age
Fig. 4: Using the distance to HD 169142 (145± 43 pc), and
assigning the spectral type to the brighter dMe star allows us to
place the pair in the HR diagram. Following Weinberger et al.
(2000) in Teff calibration, and using the models of Baraffe et al.
(1998), we find 2MASS 18242929-2946559 is coeval with HR
4796 A. The estimated age agrees with independent estimates
for HD 169142 A. The presence of 3 PMS stars within 1160 AU
of each other is consistent with an aggregate similar to HD
104237.
size
This study
1.4”
inclination
<20”
structure
none
Radial surface brightness r-3
Kuhn et al. (2001)
1.5”
Raman et al. (2005)
1.6”
13º±2
Spiral feature to N
This study made use of data obtained as part of HST-GO-10177. The Goddard Fabry-Perot was supported under TBD.
Apache Point Observatory Goddard Fabry-Perot observations were made through a grant of Director's Discretionary
Time. Apache Point Observatory is operated by the Astrophysical Research Consortium.
Fig. 8: HD 169142 has a UV spectrum in good
agreement with Altair (A7V). Any UV excess is at
least a factor of 5 fainter, relative to the star than for
the accreting system HD 104237.
Fig. 9: HD 169142 also lacks the strong Mg II
emission and wind features characteristic of accreting
Herbig Ae stars. Raman et al. (2005) find an
accretion rate of 10-8 M yr-1. The available UV data
suggest that this material is not reaching the star, and
must be being intercepted either by a brown dwarf or
planetary mass body.
6. Summary
HD 169142 has newly identified T Tauri companions
which allow us to confirm that this system is an older
Herbig Ae star, comparable in age to HR 4796 A.
The circumstellar disk can be traced out to 1.4” (200
AU) and exhibits an r-3 radial surface brightness power
law, indicative of dust settling. The presence of
extended PAH emission is expected in such a
comparatively flat disk if there is a central cavity in the
disk. The presence of a cavity is supported by the low
level of the UV excess light, the weak Mg II and H
emission and the absence of a high velocity wind/jet
component similar to that seen toward other Herbig Ae
stars. Despite the presence of a large dust disk with
abundant molecular gas (Dent et al. 2005; Raman et al.
2005), the UV data suggest that comparatively little
material currently reaches the star. The central portion
of this disk would therefore appear to be a promising
environment, coupled with the face-on geometry, for
near-stellar brown dwarf or young exo-planet searches.