The (visible) (re-)birth of a star: IRAS 05436-0007 = V1647 Orionis

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Latest update: March 24, 2005

Much has happened since the last update. A brief summary of some of the news follows.

Older update: September 1, 2004

In IAUC 8396, Aspin and Reipurth report that an image taken with the Gemini guide camera on Aug 29 shows McNeil's Nebula and its central star to be "in its elevated state." I interpret this to mean "still roughly as bright as it was when it went behind the Sun," consistent with my result from Aug 22.

older update: August 27, 2004

For your viewing pleasure, a graph showing the evolution of McNeil's Nebula in the infrared, visible, and X-ray. This is a slightly updated version of one of the figures from Kastner et al. in Nature (July 22, 2004) . You can find links to local copies of that paper below, in the July 23, 2004, entry.

older update: August 25, 2004

Two items today: a new paper, and a lousy (first?) attempt to measure the optical brightness of the central star as it returns to the nighttime sky.

older update: August 18, 2004

Peregrine McGehee and coauthors describe the change in optical and near-IR colors of V1647 Orionis from its "quiescent" state to its outburst.

Vacca, Cushing and Simon present near-IR spectroscopy of the object taken on March 9, 2004, with the SpeX instrument:

older update: July 23, 2004

Lots of new stuff in the past month.

older update: June 15, 2004

The star finally has an official name! IAUC 8354 announces that the object is now called V1647 Orionis.

older update: June 12, 2004

Measurements of the new object in the mid-IR (low-res spectra between 7.5 and 12.5 microns) and sub-mm (450 and 850 microns) are reported in astro-ph 0406089 , by Andrews, Rothberg and Simon. A portion of their Abstract:

The 12 micron flux of this source has increased by a factor of 25 after the outburst, whereas the submillimeter continuum remains at its pre-outburst level. The bolometric luminosity has increased by at least an order of magnitude, to ~34 L_sun, and is likely less than 90 L_sun. The mid-infrared spectrum exhibits a strong and red continuum with no emission or absorption features. The infrared slope of the spectral energy distribution characterizes the illuminating source as a flat-spectrum protostar, in both its active and quiescent states.

Peregrine McGehee presented a poster paper on optical and near-IR photometry of the environment of the new object, both before and during outburst. A longer paper based on the data is being prepared for publication in ApJ.

Peregrine also points out that a paper discussing FU Ori outbursts in a theoretical context, astro-ph 0406264 by Lodato and Clarke, may be of interest.

older update: May 13, 2004.

Doug Finkbeiner has created new color mosaics of the field around McNeil's object, based on scans from the Sloan Digital Sky Survey . See them down below . Doug provides a warning:

Note that an asinh stretch is used ... and that the colors saturate to the correct RGB color ratio instead of to white.

older update: Apr 16, 2004.

Bruce Gary's recent I-band photometry suggests that the brightness of the object may have reached a first peak, faded just a bit, then increased slightly before starting to fade again. Could this very small secondary peak be due to light echoes, rather than an intrinsic increase in the light from the central source? Bruce has some evidence that it very well may be due to a light echo; see Bruce's speculations on a light echo, which are based on a careful analysis of the appearance of the source's Point-Spread-Function (PSF).

older update: Apr 14, 2004.

A paper by Abraham et al. has appeared on astro-ph, describing the infrared and sub-mm properties of the object:

They conclude that the object has a disk of about 0.5 solar masses, a pre-outburst bolometric luminosity of 5.6 solar, and is probably a class II protostar of age about 400,000 years.

older update: Apr 2, 2004.

The technical papers are starting to appear:

Older update: Mar 30, 2004.

You can hear Jay McNeil talk about his discovery on an audio clip from NPR's "Weekend Edition". In other news, we have learned that the Spitzer Space Infrared Telescope not only took images of the field on March 15 with the (mid-IR) MIPS instrument (we knew that already), but also took images with its (near-IR) IRAC instrument a week earlier, March 7. Unfortunately, we haven't been able to look at this data yet ...

Older update: Mar 23, 2004.

Several items today: Joel Kastner tells me that Chandra has successfully observed the object for a second time since outburst, about 15 days after the first X-ray measurement. I've predicted that the source will be more than twice as faint as it was at the earlier epoch; Joel tells me he'll be able to make a good measurement sometime within the next week or so.

I've also come across a nice, big, false-color mosaic of the M78 region which includes the new object. Go to the 2MASS Atlas Image Gallery of HII regions, star formation regions, and reflection nebulae and scroll down about halfway through the page. It was hard for me to see on the little thumbnail, but the full-size version shows the object very clearly. Note that this is based on images taken several years ago, so it's a "pre-outburst" IR image.

Old update: Mar 22, 2004.

The Gemini Observatory has put out a press release which includes some nice pictures of the star, some astronomers (including Jay McNeil), and an artist's rendition of what may be happening.

Old update: Mar 16, 2004.

Bruce Gary, of Hereford, Arizona, has been following the optical evolution of the new star since mid-February. He finds that in the R and I bands, the star has reached its peak brightness and is now starting to fade. For all the details, look at Bruce Gary's measurements of the new star.

Old update: Mar 15, 2004.

César Briceño has made a movie showing the evolution of the new star and its nebulosity in the visible part of the spectrum, based on images taken with the 1m Schmidt telescope of Llano del Hato National Astronomical Observatory in Venezuela. Go to Cesar's movie page to see the animation. Also, the Spitzer satellite acquired infrared images of the star last night.

Old update: Mar 8, 2004.

Joel Kastner reports that a Chandra X-ray image shows the new star to be much brighter than it was in the pre-outburst X-ray image. Rah! More analysis soon from Joel ....

Old update: Mar 1, 2004.

Arne Henden provides a color composite in BVI of the new object, taken Feb 22, 2004.

Old update: Feb 28, 2004.

See some color pictures of the field from 199 and 2002.

Old update: Feb 21, 2004.

Peregrine McGehee reports that the literature contains several images of the field taken in years past. You can see some scanned versions of these images and speculation on what they mean in the Feb 21 section of this page, below. There's also a very pretty color picture of the area made by David Schlegel from SDSS scans of the area.

Old update: Feb 20, 2004.

Joel Kastner describes X-ray emission from the new object in a Chandra image taken in 2002. It appears that Chandra will be looking at the new star as a Target Of Opportunity in early March!

A new star appears in early 2004

The position of the new star, based on 2MASS K-band image from 1999, is

        RA = 05:46:13.1     Dec = -00:06:05     (J2000)

In the past few weeks, a new star has appeared to our visible instruments in the Milky Way Galaxy. It's not a "nova" or "supernova" -- the result of a gigantic explosion near the end of a star's life -- but a stellar birth!

In one particular region of the Milky Way lies a giant cloud of gas and dust, which astronomers call M78.

Image courtesy of Daniel Verschatse (Antilhue Obs.)

Young stars are forming out of this cloud, and their light excites the remaining gas, causing it to glow. We call the beautiful glowing cloud a nebula.

Note that the region to the lower-right of M78 is rather dark:

In this region, the thick dusty clouds block light from stars hidden behind them. Only a few stars manage to penetrate the gloom. Because blue light is scattered and absorbed more easily than red light, these stars appear redder than they truly are.

Let's concentrate on a small region near the center of the box. Way back in 1951, astronomers photographed this region in red light as part of the Palomar Observatory Sky Survey (POSS). The image shows a few stars, with a nice pair near the center.

In 1990, a second photographic survey (POSS II) again photographed the region in red light, and found, well, pretty much the same picture. The pair of stars near the center is again the most prominent feature.

In 1998, the 2MASS project surveyed the area, this time at infrared wavelengths. Because infrared light has a longer wavelength than visible light, it ought to penetrate the dusty clouds more deeply and show us any objects hidden within. You can see several new stars, to the lower right of the bright pair, which aren't apparent in the visible-light images.

Hmmmm.... These stars must be hidden within cocoons of dust and gas.

In January, 2004, however, ordinary visible-light photographs of the region suddenly revealed a new object. The first report came from J. W. McNeil, of Paducah, Kentucky, who noticed the new object on Jan 23, 2004. Compare these two pictures taken by Japanese astronomer Yasuo Sano: in 2001, on the left, and in 2004, on the right:

The right-hand picture above was taken on February 11, 2004. The picture below, also from Sano-san, was taken one night later.

Sano-san's pictures indicate that the star is growing brighter quickly, within the span of a single day. His measurements:

     object          YYYYMMDD(UT)   mag     code
     IRAS05436-0007  20040211.455  14.46CR  San.VSOLJ
     IRAS05436-0007  20040212.421  14.07CR  San.VSOLJ

     Yasuo Sano (Nayoro, Hokkaido,Japan)
     Instruments: 28cm-SCT + ST-9E exp 30sec(2004/02/11).
                  25cm-NT + ST-9E exp 30sec(2004/02/12)
     Comparison stars: Henden 3 star R mag
Kamil Hornoch also finds that the object becomes brighter:
  Date: Fri, 13 Feb 2004 11:29:47 +0100
  From: Kamil Hornoch 
  Subject: New nebula near M78: additional photometry

  Most southern star (and brightest star included in a new nebula)
  increased its brightness of about 0.20 mag between Feb. 11.913 UT
  and 12.908 UT.

Let's compare the location of this new object in the visible to the infrared picture taken several years ago. Here's a zoomed-in view of the optical picture -- click on it to reach a "blinking" page, where you can switch back and forth between visible and IR.

Yes! The star really was there back in 1999 (and probably for thousands of years earlier), but it has just now become visible in the optical. Why? It must be blowing away the cocoon of dust and gas which surrounds it -- we think all young stars have strong winds of this kind. Over the past few years, the wind has managed to clear enough dust that the visible light emitted by this young star can finally make it all the way to Earth.

The position of the new star, based on 2MASS K-band image from 1999, is

        RA = 05:46:13.1     Dec = -00:06:05     (J2000)

Arne Henden provides a nice R-band image of the new star taken with the 1.0-m telescope at US Naval Observatory in Flagstaff, Arizona. He also provides photometric calibration for some of the nearby stars -- see the table below.

This is just a small sample of Arne's measurements for a subset of stars marked in the chart. See the full table with all the data below.

ID     RA        Dec          V      B-V   U-B     V-R   R-I
A   86.581120  -0.088877    14.853  1.577 99.999  1.081 1.081     LkHA 301
B   86.578727  -0.093920    16.290  1.847 99.999  1.279 1.345     variable?
C   86.485580  -0.182250    14.971  1.137 99.999  0.713 0.609 

Gianluca Masi points out that star "B" is apparently variable in brightness. Taichi Kato and Brian Skiff mention that this star exhibits emission lines, and may very well be a T Tauri variable. The companion, star "A", also known as LkHA 301, is a known T Tauri star, and a variable. It is not surprising to find very young (and variable) stars in this star-forming region.

Added Feb 13, 2004, EST.

Gianluca Masi notes that this object was apparent in the optical several decades ago. He writes:

the object was observed two days ago by me and Franco Mallia, using the Tenagra II telescope. The star was really evident (the images were grabbed around 11.2 feb UT) and its astrometry reported to CBAT. Here is the image:

I have also found an image of 1960s where the same feature is visible. This seems to suggest a repeated outburst of the source.

I've sent a report to CBAT. I saw evidence of the "nebula" starting on Nov 2003, since then showing an incresing brightness.

I suggest to closely monitor the object for the remaining season.

Gianluca points to this image of M78 (left below), part of the SEDS Messier gallery, available at The photograph is part of the book The Messier Album, by John H. Mallas and Evered Kreimer, published in 1978 by Cambridge University Press. The image was taken by Kreimer from his home in Prescott, AZ, (alt 5400 feet), on Oct 22, 1966 with a 12.5-inch f/7 Cave reflector, a 15-minute exposure only Tri-X cooled to -109 F in a dry-ice camera. The film was processed in D-19 for 4 minutes, and (alas) a dodging mask was used in making the print. Tri-X peaks in the blue part of the spectrum.

The image on the left is the "old" one, from 1966; the image on the right is a half-size version of Sano-san's picture of Feb 12, 2004. Note that the nebulosity in 1966 is brightest at the top (north) end, whereas the 2004 event is brightest at the bottom.

Added Feb 15, 2004

Brian Skiff warns that it won't be easy to make accurate meassurements of the new star's brightness:

Because of the very strong reddening of this star, it will almost certainly be necessary for folks to use standard photometric filters, since color terms among various chips and varying temperatures etc on the same chip will be impossible to compensate for.

In addition, without the additional information of the the photometric aperture used, as well as details on how the strong and strongly-varying background has been dealt with, comparisons among different observers will be unworkable.

Large image scales (long focal-length and small pixels) will be required to deal with this star. The gradient of the nebula near the star might be modelled by a tilted plane (or quadratic) to determine the sky level at the star itself. Annular 'sky' zones probably won't work. The 'star' apertures will have to be very small (few arcsec only).

Added Feb 17, 2004

At last the big guys have become involved. Aspin and Reipurth report that near-IR images taken with the Gemini 8-m telescope show that the object has brightened by about 3 magnitudes in JHK, relative to the 1998 2MASS measurements. Gemini spectra reveal strong features of CO and hydrogen Brackett-gamma in emission in the IR; in the optical, H-alpha shows emission with a P Cygni profile.

Suggested readings for reports of similar events:

Added Feb 19, 2004

The Sloan Digital Sky Survey detected a very faint source at the position of the new star several times in the past few years. Here's an image taken in early February, 2002, in the z-band; (the SDSS z-band has an effective wavelength of about 8950 Angstroms and a width of about 1140 Angstroms).

A closeup shows the object clearly, plus some very faint emission from nebulosity to its north.

Added Feb 20, 2004

Selected tidbits from IAU Circular 8290:

Which brings us chronologically to the first person who apparently noticed something out of the ordinary: amateur astronomer Jay McNeil, who first noticed the recent outburst in an image taken on January 23, 2004. You can read Jay McNeil's own account of the events (and my local copy ). in the February, 2004, issue of the Houston Astronomical Society's newsletter. Astronomy Picture of the Day has chosen this new object as its topic for their entry for Feb 19, 2004. APOD also provides a nice color picture taken by Adam Block as part of the Kitt Peak National Observatory Visitor Program. A larger version can be found in the APOD entry for Feb 19, 2004.

Here's a closeup of an X-ray image near the new star, courtesy of Joel Kastner and the Chandra data archive. The field is about 4x4 arcminutes, with North up and East to the left. The new object is the very weak source at center; stars A and B are the bright pair to its north-east, as in optical and IR images.

Added Feb 21, 2004

Peregrine McGehee points out a couple of existing papers which discuss the new object and its neighbors:

A color picture from the SDSS appears at the end of today's section.

Here's a chart from the paper by Eisloffel and Mundt showing [SII] emission from the area. North is up, East to the left. The two stars just to the left of the label "HH22" are the ones I've called "A" and "B" in charts above. Watch out for some image distortion on the left -- I couldn't get the page to sit flat on the scanner's platen :-(

A closeup around the new object's area: [SII] on the left, from October, 1995, and R-band on the right, from mid-Feb, 2004:

Zoom in even closer: again, [SII] from 1995 on the left, R-band from Feb 2004 on the right:

A deeper image from the paper shows the region around the new star more clearly; click on the image below for a larger version.

As Eisloffel and Mundt state, what we see to the right (west) of the double star is a combination of two different sources:

  1. the bright knot of nebulosity due west of the double stars, marked "A" in the chart above, lies at the end of a jet, marked by a series of condensations. This jet presumably originates in a star somewhere to the east (left) of the chain, but Eisloffel and Mundt couldn't find any source in the right place

  2. the nebulosity labelled "HH23", to the north of the double stars, appears to be the terminus of a jet coming from the south. It looks like the source might be near the cross, which marks the infrared source IRAS 05436-0007. That is also the location of the new star which has just recently become visible in the optical.

These images suggest (to me, at least) that the blob of nebulosity "A" just north of the new star may not be coupled to it directly; it may very well be in the foreground or background. However, on the other hand, when we go back to look at Kreimer's image back in 1966 (shown below at far right) we see that BOTH the southern core (corresponding to the IRAS source and newly visible star) AND the northern blob "A" both appear bright!

So this is a mystery: if the knot "A" belongs to the west-going jet from HH22, and the new star makes a north-going jet upwards towards HH23, why should both knot "A" and the new star appear brighter than usual at the same time back in 1966? Is it possible that the knot "A" is a product of both outflows, which happen to run into each other by some coincidence?

On to the paper on infrared imaging by Lis et al.. Their figure 5 shows the area around HH22, taken in January 1997:

Let's compare it to the [SII] image of Eisloffel and Mundt:

It seems that

Lis et al. provide measurements of LMZ 12 at several passbands in the far-IR in their Figure 6: the two longest, 350 and 1300 microns, they determined themselves in January, 1997; the four other data are taken from IRAS, which observed the area sometime in the early 1980s. Lis et al. describe how they were unsatisfied with the IRAS catalog entry at 60 microns and re-derived the flux at that wavelength. Given what we know now about the variability of the object, it's not clear that combining measurements taken 15 years apart is a good idea.

This color composite comes from the Sloan Digital Sky Survey: blue = the 'g' filter (centered on 4700 Angstroms), green = the 'r' filter (6200 Angstroms, includes H-alpha), red = the 'i' filter (7500 Angstroms). Thanks to David Schlegel and Jill Knapp for providing it! Click on the image for the full-size version.

Added Feb 28, 2004

Thanks to Steve Kent and the Sloan Digital Sky Survey , here are two pictures of the field from a few years back: one from 1998 and another from 2002.

Taken in November, 1998:

Taken in February, 2002:

Added Mar 1, 2004

Arne Henden has made a nice color composite from images in B, V and I, taken with the USNO 1.55 m telescope on Feb 22, 2004. Click on the image below for a full-size version.

Added May 13, 2004

Doug Finkbeiner provides _big_ color mosaics from the Sloan Digital Sky Survey. Click on each thumbnail to download the full image. Beware -- they are around 8 MB each!

First, a composite of the g, r, i passbands:

Next, a composite of the r, i, z passbands (which go into the near-infrared):

For more information