Proper motions and variabilities of stars near the Orion Nebula

Jones, B. F.; Walker, Merle F.

doi:10.1086/114773

Cited by 259 publications

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“…The resulting velocity dispersion of our model is lower than the observational value (σ = 4.3 ± 0.5 km s −1 : Jones & Walker 1988). However, because of significant mass of the molecular cloud associated with the ONC that was neglected in our numerical model, the observed velocity dispersion is consistent without any assumption about a stellar system in dynamical equilibrium.…”

Section: Methods and Cluster Setupmentioning

confidence: 42%

Evolution of the binary population in young dense star clusters

Kaczmarek

Olczak

Pfalzner

2011

A&A

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Context. Field stars are not always single stars, but can often be found in bound double systems. Since binary frequencies in the birth places of stars, young embedded clusters, are sometimes even higher than on average the question arises of how binary stars form in young dense star clusters and how their properties evolve to those observed in the field population. Aims. We assess, the influence of stellar dynamical interactions on the primordial binary population in young dense cluster environments. Methods. We perform numerical N-body simulations of the Orion nebula cluster like star cluster models including primordial binary populations using the simulation code nbody6 ++ . Results. We find two remarkable results that have yet not been reported: The first is that the evolution of the binary frequency in young dense star clusters is independent predictably of its initial value. The time evolution of the normalized number of binary systems has a fundamental shape. The second main result is that the mass of the primary star is of vital importance to the evolution of the binary. The more massive a primary star, the lower the probability that the binary is destroyed by gravitational interactions. This results in a higher binary frequency for stars more massive than 2 M compared to the binary frequency of lower mass stars. The observed increase in the binary frequency with primary mass is therefore most likely not due to differences in the formation process but can be entirely explained as a dynamical effect. Conclusions. Our results allow us to draw conclusions about the past and the future number of binary systems in young dense star clusters and demonstrate that the present field stellar population has been influenced significantly by its natal environments.

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Section: Methods and Cluster Setupmentioning

confidence: 42%

Evolution of the binary population in young dense star clusters

Kaczmarek

Olczak

Pfalzner

2011

A&A

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“…They find a proper motion of 9.5 km s −1 in RA and −3 km s −1 in Dec, what leads to a total velocity of ∼10 km s −1 well consistent with our velocity measurement. The velocity dispersion of the stars in the ONC has been estimated to be ≈2.3 km s −1 (Jones & Walker 1988) assuming a distance of 470 pc. For a distance of 414 pc this scales to a velocity dispersion of 2.0 km s −1 .…”

Section: θ 1 Ori Amentioning

confidence: 99%

The multiplicity of massive stars in the Orion Nebula Cluster as seen with long-baseline interferometry

Grellmann

Preibisch

Ratzka

et al. 2013

A&A

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Context. The characterization of multiple stellar systems is an important ingredient for testing current star formation models. Stars are more often found in multiple systems, the more massive they are. A complete knowledge of the multiplicity of high-mass stars over the full range of orbit separations is thus essential to understand their still debated formation process. Aims. Infrared long baseline interferometry is very well suited to close the gap between spectroscopic and adaptive optics searches. Observations of the Orion Nebula Cluster (ONC) in general and the Trapezium Cluster in particular can help to answer the question about the origin and evolution of multiple stars. Earlier studies provide a good knowledge about the multiplicity of the stars at very small (spectroscopic companions) and large separations (AO, speckle companions) and thus make the ONC a good target for such a project. Methods. We used the near infrared interferometric instrument AMBER at ESOs Very Large Telescope Interferometer to observe a sample of bright stars in the ONC. We complement our data set by archival NACO observations of θ 1 Ori A to obtain more information about the orbit of the close visual companion. Results. Our observations resolve the known multiple systems θ 1 Ori C and θ 1 Ori A and provide new orbit points, which confirm the predicted orbit and the determined stellar parameters for θ 1 Ori C. Combining AMBER and NACO data for θ 1 Ori A we were able to follow the (orbital) motion of the companion from 2003 to 2011. We furthermore find hints for a companion around θ 1 Ori D, whose existence has been suggested already before, and a previously unknown companion to NU Ori. With a probability of ∼90% we can exclude further companions with masses of ≥3 M around our sample stars for separations between ∼2 mas and ∼110 mas. Conclusions. We conclude that the companion around θ 1 Ori A is most likely physically related to the primary star and not only a chance projected star. The newly discovered possible companions further increase the multiplicity in the ONC. For our sample of two O and three B-type stars we find on average 2.5 known companions per primary, which is around five times more than for low-mass stars.

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“…We selected from Hillenbrand (1997) 96 stars with a membership probability given by Jones & Walker (1988) higher than 95%. Their spatial location is shown in Fig.…”

Section: Sample Selection and Observationsmentioning

confidence: 99%

Evidence of early disk-locking among low-mass members of the Orion Nebula Cluster

Biazzo

Melo

Pasquini

et al. 2009

A&A

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Context. We present new high-resolution spectroscopic observations for 91 pre-main sequence stars in the Orion Nebular Cluster (ONC) with masses in the range 0.10−0.25 M carried out with the multi-fiber spectrograph flames attached to the UT2 at the Paranal Observatory. Aims. Our aim is to better understand the disk-locking scenario in very low-mass stars. Methods. We have derived radial velocities, projected rotational velocities, and full width at 10% of the Hα emission peak. Using published measurements of infrared excess (Δ(I C − K)), as disk tracer and equivalent width of the nead-infrared Ca ii line λ8542, mid-infrared difference [3.6]-[8.0] μm derived by Spitzer data, and 10% Hα width as diagnostic of the level of accretion, we looked for any correlation between projected angular rotational velocity divided by the radius (v sin i/R) and presence of disk and accretion. Results. For 4 low-mass stars, the cross-correlation function is clearly double-lined, indicating that the stars are SB2 systems. The distribution of rotation periods derived from our v sin i measurements is unimodal with a peak of a few days, in agreement with previous results for M < 0.25 M . The photometric periods were combined with our v sin i to derive the equatorial velocity and the distribution of rotational axes. Our sin i is lower than the one expected for a random distribution, as previously found. We find no evidence of a population of fast rotators close to the break-up velocity. A clear correlation between v sin i/R and Δ(I C − K) has been found. While a spread in the rotation rates is seen for stars with no circumstellar disk (Δ(I C − K) < 0.3), stars with a circumstellar disk (Δ(I C − K) > 0.3) show an abrupt drop in their rotation rates by a factor of ∼5. On the other hand, only a partial correlation between v sin i and accretion is observed when other indicators are used. The X-ray coronal activity level (log L X /L bol ) shows no dependence on v sin i/R, suggesting that all stars are in a saturated regime limit. The critical velocity is probably below our v sin i detection limit of 9 km s −1 . Conclusions. The ONC low-mass stars in our sample, close to the hydrogen burning limit, at present do not seem to be locked, but the clear correlation we find between rotation and infrared color excess suggests that they were locked once. In addition, the percentage of accretors seems to scale inversely to the stellar mass.

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Proper motions and variabilities of stars near the Orion Nebula

Cited by 259 publications

References 0 publications

Evolution of the binary population in young dense star clusters

Evolution of the binary population in young dense star clusters

The multiplicity of massive stars in the Orion Nebula Cluster as seen with long-baseline interferometry

Evidence of early disk-locking among low-mass members of the Orion Nebula Cluster

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