A Variable Nebula Associated with HBC 340 and HBC 341
A refereed publication on this material was produced by Dahm & Hillenbrand (2017) -
abstract.
The story is below.
Amateur astronomers working as "astroteamCERES" in Switzerland
identified in October of 2014 that a nebular structure in
NGC 1333 associated with the known young stars
HBC 340
and
HBC 341
had changed appearance.
Rainer Spaeni, Christian Rusch, and Egon Eisenring found that the nebula
had faded relative to previous images from 2012,
but that by November and December of 2014
it had returned to its previous brightness.
The Palomar Transient Factory
has been observing the NGC 1333 field over several seasons
and has also detected variations in the nebular structure, as announced in
an issued ATel
and illustrated in the movie below
(fading starts at about 1/3 of video length).
We attribute the nebular variations to variable illumination by HBC 340.
The light echo situation is probably similar to the famous
``Hubble's variable nebula" (also known as NGC 2261)
located in the young cluster NGC 2264 and which is
variably illuminated by the young star R Mon.
Some nice movies of this source are
here and
here .
Another example is LRLL 54361 which is a periodically
variable protostar and nebula
In each case,
the conical or fan-shaped nebula likely indicates a cavity in the
circumstellar environment that has been evacuated by outflowing material
from the rapidly accreting young star at its base.
From the PTF image archive, 124 images covering a ~300" x 300" field
were obtained and corrected both for positional registration
(using the average offset derived from the weighted average centroids
of the five brightest stars) and flux differences (based on the mean offsets
of sky-subtracted photometry for the same five bright stars).
The comparison stars are denoted by the circles in the image below;
they range in brightness from R_PTF = 14.5 to 16.5 mag. Their measured scatter
over the PTF time series ranges from 0.01 to 0.07 mag, which is higher
than expected for the apparent magnitudes since most are also young stars
with intrinsic variability. But considering the averaging,
the relative photometric calibration should be reasonably precise.
The extracted R_PTF lightcurves for HBC 340 (southern brighter source) and HBC 341 (northern fainter source)
are shown below. With the pair separation only ~5", the fainter star photometry is contaminated by the brighter star,
despite the attempt to use as small an aperture as possible;
thus although we believe based on the video that both stars are variable,
the correlations in brightness between the two likely are not real.
HBC 340 appears to be the more dramatic variable of the pair,
with changes of 1-2 mag on time scales of a week to several months.
The two nebular fading episodes in the movie correspond to the two minima
in the light curve around JD 2456630 and JD 2456885.
An alternate version of the movie shown above, now correlated (via the moving red line)
with the point source light curves:
The nebular fading behavior appears to be an ongoing phenomenon over at least several decades.
Lick Observatory plates shown by Herbig (1974; Lick Obs. Bull. 658; Figures 1/2)
illustrate a state in which the eastern side of the nebula is faint, while the western side
is bright, similar to some epochs of the PTF data stream when the source is entering
or recovering from the deep minima when the nebula disappears entirely.
Herbig's plate data taken in 1959 at the 120" is shown below. The faint nebulous knot that is
aligned with HBC 340 and HBC 341 just to the northeast, is not readily apparent in our Palomar 48" data
except perhaps in the best seeing frame.
It is suggested that the newly appreciated nature of the nebula
could warrant it being known in the future
as the NGC 1333 Rusch-Eisenring-Spaeni variable nebula (or RESVN),
after the discoverers of its morphological changes on few month time scales.
