Orion Measurements Change Stellar Ages

by Paul Gilster on October 9, 2007

Following up on our recent discussion of interstellar distances and how they are determined comes word of a reassessment of the distance to the Orion Nebula. The star forming region is famous not only for its beauty but for the opportunity it gives us to assess young stars as they emerge from the interstellar gases around them. Their distance tells us something about their intrinsic brightness and thus their ages.

The change in distance revealed in the new studies is considerable. Whereas the previous best estimate to the Nebula was 1565 light years, the new one, drawn with an uncertainty of six percent, is 1270 light years, a twenty percent adjustment. The Very Long Baseline Array was behind this work, using familiar parallax methods to observe a star called GMR A from opposite sides of Earth’s orbit.

“This measurement is four times more precise than previous distance estimates,” says Geoff Bower (UC-Berkeley). “Because our measurement reduces the distance to this region, it tells us that the stars there are less bright than thought before, and changes the estimates of their ages.”

And what a change. These stars are twice as old as once thought.

What we’re still doing — and we’re early in the process — is getting an approximation of the three-dimensional structure of nearby interstellar space. VLBA is ideal for this work because its ten 25-meter radiotelescope dishes stretch from the Pacific (Hawaii) to the Caribbean (Virgin Islands), allowing it to produce images of remarkably high resolution. Huge amounts of work remain to be done as we adjust distances to various targets. It’s amazing to consider that if we somehow found a way to reach the stars tomorrow, we’d still be faced with the same conundrum experienced by sailors in the 16th Century, the absence of reliable maps.

VLBA has also made observations of star-forming regions in Taurus and Ophiuchus as well as examinations of the Milky Way’s spiral arms and pulsars. With operations managed from Socorro, New Mexico, it’s the world’s largest dedicated, full-time astronomical instrument. The new findings appear as Sandstrom et al., “A Parallactic Distance of 389 +24/-21 parsecs to the Orion Nebula Cluster from Very Long Baseline Array Observations,” accepted by The Astrophysical Journal (abstract).

philw1776 October 15, 2007 at 15:53

Once again we see that what we THOUGHT science told us was not quite so. Stay humble as more paradigms will be overturned. That of course is the intrinsic method of science.

forrest noble October 30, 2007 at 2:54

philw1776, I agree with your sentiments 100% but wish to go you one better. Not only the stars in this galaxy are twice as old as previously thought, I believe the stars in most galaxies are much older than previous estimates including our own– meaning the observable universe is also much older.

ljk December 19, 2007 at 12:44

X-ray properties of protostars in the Orion Nebula

Authors: L. Prisinzano (1), G. Micela (1), E. Flaccomio (1), J. R. Stauffer (2), T. Megeath (3), L. Rebull (2), M. Robberto (4), K. Smith (4), E. D. Feigelson (5), N. Grosso (6), S. Wolk (7) ((1) INAF – Osservatorio Astronomico di Palermo, Italy (2) Spitzer Science Center, California Institute of Technology, Pasadena, CA (3) Department of Physics, University of Toledo, OH (4) Space Telescope Science Institute, Baltimore, MD (5) Department of Astronomy and Astrophysics, Penn State University PA, USA (6) Observatoire astronomique de Strasbourg, Universite’ Louis-Pasteur, CNRS, INSU, Strasbourg, France (7) Harvard Smithsonian Center for Astrophysics, Cambridge)

(Submitted on 18 Dec 2007)

Abstract: The origin and evolution of the X-rays in very young stellar objects (YSOs) are not yet well understood since it is very hard to observe YSOs in the protostellar phase. We study the X-ray properties of Class 0-I objects in the Orion Nebula Cluster (ONC) and compare them with those of the more evolved Class II and III members. Using Chandra Orion Ultradeep Project (COUP) data, we study the X-ray properties of stars in different evolutionary classes: luminosities, NH, temperatures and time variability are compared in order to understand if the interaction between the circumstellar material and the central object can influence the X-ray emission. We have assembled the deepest and most complete photometric catalog of objects in the ONC region from the UV to 8 microns using data from HST, WFI@2.2m ESO and ISPI@4m CTIO telescopes, and Spitzer IRAC. We select high probability candidate Class 0-I protostars, distinguishing between those having a spectral energy distribution which rises from K up to 8 microns (Class 0-Ia) from those where the SED rises from K up to 4.5 microns and decreasing afterwards (Class 0-Ib). We select a sample of bona fide Class II stars and a set of Class III stars with IR emission consistent with normal photospheres. Our principal result is that Class 0-Ia objects are significantly less luminous in X-rays, both in the total and hard bands, than the more evolved Class II stars with mass larger than 0.5 Msun; these latter show X-ray luminosities similar to those of Class 0-Ib stars. This result supports the hypothesis that the onset of X-ray emission occurs at a very early stage of star formation. Temporal variability and spectral properties of Class 0-I stars are similar to those of the more evolved Class II and III objects, except for a larger absorption likely due to gas in the circumstellar material.

Comments: Comments: 38 pages, 14 Postscript figures, 14 Tables. Accepted for publication in ApJ

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0712.2975v1 [astro-ph]

Submission history

From: Loredana Prisinzano [view email]

[v1] Tue, 18 Dec 2007 15:14:15 GMT (665kb)


ljk March 19, 2008 at 18:49

Discovery of two magnetic massive stars in the Orion Nebula Cluster: a clue to the origin of neutron star magnetic fields?

Authors: V. Petit, G.A. Wade, L. Drissen, T. Montmerle, E. Alecian

(Submitted on 18 Mar 2008)

Abstract: The origin of the magnetic fields in neutron stars, and the physical differences between magnetars and strongly magnetised radio pulsars are still under vigorous debate. It has been suggested that the properties of the progenitors of neutron stars (the massive OB stars), such as rotation, magnetic fields and mass, may play an important role in the outcome of core collapse leading to type II SNe. Therefore, knowing the magnetic properties of the progenitor OB stars would be an important asset for constraining models of stellar evolution leading to the birth of a neutron star.

We present here the beginning of a broad study with the goal of characterising the magnetic properties of main sequence massive OB stars. We report the detection of two new massive magnetic stars in the Orion Nebula Cluster: Par 1772 (HD 36982) and NU Ori (HD 37061), for which the estimated dipole polar strengths, with 1 sigma error bars, are 1150 (+320,-200) G and 650 (+220,-170) G respectively.

Comments: Accepted by MNRAS

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0803.2691v1 [astro-ph]

Submission history

From: V\’eronique Petit [view email]

[v1] Tue, 18 Mar 2008 18:05:54 GMT (1380kb)


ljk April 2, 2008 at 10:27

Proplyds and Massive Disks in the Orion Nebula Cluster Imaged with CARMA and SMA

Authors: J. A. Eisner, R. L. Plambeck, John M. Carpenter, S. A. Corder, C. Qi, D. Wilner

(Submitted on 21 Mar 2008)

Abstract: [Abridged] We imaged a 2′ x 2′ region of the Orion Nebula cluster in 1.3 mm wavelength continuum emission with the recently commissioned Combined Array for Research in Millimeter Astronomy (CARMA) and with the Submillimeter Array (SMA). Our mosaics include >250 known near-IR cluster members, of which 36 are so-called “proplyds” that have been imaged previously with the Hubble Space Telescope. We detected 40 sources in 1 mm continuum emission, and several of them are spatially resolved with our observations. Dust masses inferred for detected sources range from 0.01 to 0.5 Msun, and the average disk mass for undetected sources is estimated to be ~0.001 Msun, approximately an order of magnitude smaller than the minimum mass solar nebula. Most stars in the ONC thus do not appear to currently possess sufficient mass in small dust grains to form Jupiter-mass (or larger) planets. Comparison with previous results for younger and older regions indicates that massive disks evolve significantly on ~Myr timescales. We also show that the percentage of stars in Orion surrounded by disks more massive than ~0.01 Msun is substantially lower than in Taurus, indicating that environment has an impact on the disk mass distribution. Finally, we explore potential correlations of disk mass with stellar mass and location within the cluster.

Comments: 45 pages, 11 figures. Accepted for publication in ApJ

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0803.3217v1 [astro-ph]

Submission history

From: Joshua Eisner [view email]

[v1] Fri, 21 Mar 2008 20:00:10 GMT (310kb)


ljk May 7, 2008 at 8:40

Near-infrared polarization images of the Orion proplyds

Authors: S. Rost, A. Eckart, T. Ott

(Submitted on 5 May 2008)

Abstract: We performed AO-assisted high-resolution imaging polarimetry on selected Orion proplyds close to the Trapezium stars in the J, H, and K bands. Differential polarimetric images of one of the largest and brightest proplyds are interpreted using 3D radiation transfer simulations based on the Monte Carlo method. Although not fully resolvable by ground-based observations, the circumstellar material can be mapped with polarimetry.

We present constraints on the disk parameters of the giant proplyd 177-341. We tested whether dust models with different grain size distributions could explain the observed extent of the polarization patterns and find that simple models with larger grains will not reproduce the spectral polarization behavior. The technique of polarimetric differential imaging (PDI) in the NIR provides a good opportunity to study the structure of the Orion proplyds.

Comments: 10 pages, 11 figures, 4 online figures

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0805.0605v1 [astro-ph]

Submission history

From: Steffen Rost [view email]

[v1] Mon, 5 May 2008 21:03:24 GMT (912kb)


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