IPHASX J052531.2+281946: a new PN towards the Galactic
Anticenter
Mampaso,
1
A. ,
1
K. ,
2
M. ,
3
M. ,
Viironen,
Corradi, R. L.
Rodríguez,
and the IPHAS Collaboration (*)
1 IAC (Tenerife, Spain), 2 ING (La Palma, Spain), 3 INAOE (Puebla, México)
Abstract and Conclusions
Observations of IPHASX J052531.2+281946
A new Planetary Nebula (PNG 178.13-04.04) has been
discovered in the course of an Hα survey of the Galactic
Plane; it has been confirmed via optical spectra. It is
near to the Anticenter direction: the third nearest known
PN toward the Anticenter. Its small diameter, and low Hβ
brigthness point to an extremely large distance; the
"Shklovskii" galactocentric distance of Dgc =14-20 kpc
renders this nebula as one of the farthest galactic PNe
where chemical abundances has been measured.
IPHAS detected several hundred strong Hα-emission
candidates located in a 30 x 10 square degree region
around the Anticenter. Most are spurious detections,
stars, and known Hα-emitting objects; however some
are "bona-fide" small nebula candidates that we are
currently studying. One of the first nebulae to be
discovered is IPHASX J052531.2+281946. Fig. 1 and 2
show the INT IPHAS Hα (top) and I (bottom) images of
the object (N is up and E to the left. The size of the box
is 1 arcmin).
Spectra were obtained on October 2004 at San Pedro
Mártir Observatory (Observatorio Astronómico Nacional,
México) with the 2.1m telescope and the B&Ch lowresolution spectrograph (2 Å/pix from 3720 to 7470 Å;
Fig. 2, top) plus the MESCAL medium-resolution echelle
spectrograph (0.1 Å /pix at the Hα region; Fig. 3, bottom
).
The IPHAS Survey
The Isaac Newton telescope Photometric Hα survey
(IPHAS; http://astro.ic.ac.uk/Research/Halpha/North/) is
currently mapping 1800 square degrees of the Northern
Galactic plane (a band between l= -5 to +5 degrees)
using the INT Wide Field Camera at the Observatorio
del Roque de los Muchachos (La Palma, Spain). The
survey is an international collaboration among 13
institutes led by J. Drew at Imperial College (London,
UK). IPHAS started in August 2003 and is expected to
be completed at the end of 2006, with an estimated total
of 30 observing weeks (mostly bright nights) shared by
the three communities involved, UK, Spain and the
Netherlands. A narrow-band Hα and two Sloan R, I
filters are used for matched 120, 30, and 10 s
exposures, respectively, spanning the range R=13 to 20
mag for point sources.
IPHAS is the first fully-photometric Hα survey of the
Galactic plane. It will discover around 40,000 new
emission-line stars, including young stars (T Tau, Herbig
AeBe stars, etc.), evolved ones (post-AGB, LBVs, etc.)
as well as binaries (CVs, symbiotic stars, etc.) in
addition to thousands of extended nebulae such as
planetary nebulae (PNe), H-H objects, HII regions, SN
remnants, etc., (Drew et al., 2005. MNRAS in press).
Physico-chemical analysis
Nebular expansion, systemic velocity and distance.
IPHASX J052531.2+281946 is a moderately reddened
(Av=1.5 mag) low density (Ne[SII]=330 cm-3) planetary
nebula. The electron temperatures are Te[NII]= 13,000
K and Te[OIII]= 10,000 K, the latter being more
uncertain given the faintness of the [OIII] λ 4363 Å line.
Ionic and total abundances are calculated with a twozone analysis using the Ionization Correction Factor
method as described by e.g. Kingsburgh and Barlow
(1994; MNRAS 271, 257).
Chemical abundances
(12+log X/H) are typical of Peimbert's Type II PNe: He/H
= 11.12; O/H = 8.55; N/H = 7.90; Ne/H = 8.19; S/H =
6.59; Ar/H = 6.19.
The velocity-position diagram shows a 12 arcsec diameter shell expanding at 17 km/s. Its radial velocity,
corrected for the Local Standard of Rest motion, is 13.5 km/s, i.e. near zero, as expected from the position of
the PN, very close to the Anticenter direction. Obviously, kinematical distances are unreliable at this region.
The distance to IPHASX J052531.2+281946 is unknown. A crude estimation can be attempted using the
"Shklovskii" statistical method, assuming a constant mass for the ionized gas of the PNe. Total Hβ flux was
measured (using a very wide slit at the B&Ch spectrograph) and dereddened with Av=1.5 mag, giving F(Hβ) =
1,7 10-13 erg/cm2 s. This locates the PN at D =12.2 kpc if an "average" nebular mass of 0.4 Mo is assumed
(c.f. Pottasch, 1984, in “Planetary Nebulae”) or D =7.0 kpc if an extremely low mass of 0.1 Mo is adopted. The
corresponding galactocentric distances are Dgc = 20, and 14 kpc, respectively. In any case, IPHASX
J052531.2+281946 is located at the same galactocentric distance or farther than any previously known PN for
which chemical abundances have been determined (Dgc =14.1 kpc; Costa et al. 2004; A&A 423, 199).
(*) The IPHAS collaborators are: Bristol University (UK): M. Masheder, S. Phillipps, R. A. H. Morris. CASU, Cambridge (UK): M. Irwin, N. Walton. Granada University (Spain): A. Zurita. Harvard-Smithsonian
Center for Astrophysics (USA): J. Drake, J. Sokoloski, D. Steeghs. Imperial College London (UK): J. Drew, Y. Unruh, E. C. Hopewell, J. S. Vink. Instituto de Astrofisica de Canarias (Spain) : A. Mampaso, K.
Viironen, E. Martin, P. Rodríguez-Gil. Isaac Newton Group (Spain): R. Corradi, R. Greimel, P. Leisy, D. Lennon, I. Skillen. Macquarie University (Australia): Q. Parker. Nijmegen University (Netherlands): P. Groot.
L. Morales-Rueda, G. Roelofs. Southampton University (UK): C. Knigge, A. Witham. University College London (UK) M. Barlow, A. Hales, N. Wright. UMIST (UK): A. Zijlstra, M. Matsuura. Warwick University (UK):
B. Gaensicke, A. Aungwerojwit
Acknowledgements: We thank J.A. López for kindly acquiring the MESCAL spectra for us.
Background image: IPHAS mosaic of IC 1396B (credits: Nick Wright,