Empirical Studies of Star Formation Below Main Sequence

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Empirical Studies of Star Formation: “Below Main Sequence” Stars, Age Spreads and Photometric Variability

Empirical Studies of Star Formation: “Below Main Sequence” Stars, Age Spreads and Photometric Variability John R. Stauffer IPAC, Head of Science Staff Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

Steve’s 1 st Paper on YSO’s • Strom, Strom et al. - 1972, Ap.

Steve’s 1 st Paper on YSO’s • Strom, Strom et al. - 1972, Ap. J 171, 267. • Optical and IR photometry in order to determine the time spread of star formation • Found IR excesses due to disks, blue excesses due to chromospheres(? ), and “below main sequence” stars • Put limits on age spread, but because of the above “features”, learned that determining the age spread in star forming regions was hard. • We still debate these issues - Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

NGC 2264 Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

NGC 2264 Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

NGC 2264 - age spread? Strom. Fest Westward Look Resort April 4 -5, 2008

NGC 2264 - age spread? Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

W 90 - The Prototype BMS star • An A 0 spectral type member

W 90 - The Prototype BMS star • An A 0 spectral type member of NGC 2264 that falls about 2. 5 mag below the ZAMS (in a V vs. B-V CMD) • E(B-V) determined to be small • Gravity consistent with PMS nature • L and 10 micron excesses • Can’t be just relatively old (since below ZAMS) • Best explained as an edge on disk • What would Steve and Karen have done if they had access to Spitzer? Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

NGC 2264 - K band excesses? Strom. Fest Westward Look Resort April 4 -5,

NGC 2264 - K band excesses? Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

N 2264 - Disks better detected at L than K Strom. Fest Westward Look

N 2264 - Disks better detected at L than K Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

35 Years Later - IRAC & N 2264 Strom. Fest Westward Look Resort April

35 Years Later - IRAC & N 2264 Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

N 2264 - IRAC 8 micron excesses Strom. Fest Westward Look Resort April 4

N 2264 - IRAC 8 micron excesses Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

Steve’s stars in Lori’s Diagram Strom. Fest Westward Look Resort April 4 -5, 2008

Steve’s stars in Lori’s Diagram Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

IRS Low Res Spectrum for W 90 Strom. Fest Westward Look Resort April 4

IRS Low Res Spectrum for W 90 Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

Robitaille Models for W 90 Strom. Fest Westward Look Resort April 4 -5, 2008

Robitaille Models for W 90 Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

W 90 in 2008 • There is now a lot of new Spitzer (and

W 90 in 2008 • There is now a lot of new Spitzer (and probably other) data for W 90, as well as much better modelling tools. • Someone should write a paper on W 90 - is it now a “well-understood” star? Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

New BMS Stars in NGC 2264 • THE INITIAL MASS FUNCTION AND YOUNG BROWN

New BMS Stars in NGC 2264 • THE INITIAL MASS FUNCTION AND YOUNG BROWN DWARF CANDIDATES IN NGC 2264. III. PHOTOMETRIC DATA Sung, Bessell, et al. AJ 135, 441, 2008 ABSTRACT. We have performed deep wide-field CCD photometry of the young open cluster NGC 2264 to study the extent of star-forming regions (SFRs) and the shape of the initial mass function. In this paper, we present VRI and Halpha photometry for more than 67, 000 stars. From the spatial distribution of the selected H? emission stars, we identify two active SFRs and a less active halo region surrounding these two SFRs. There are several Halpha emission stars in the field region outside the halo region, and these may be newly formed stars in the Mon OB 1 association surrounding the cluster. The locus of pre -main-sequence (PMS) stars in the IC versus V - IC diagram is revised from the distribution of Halpha and X-ray emission stars in the diagram. The mean reddening of late-type PMS stars is estimated to be E(B - V) ~ 0. 2 mag using the distribution of X-ray emission stars in the 2 MASS color diagram. We can confirm that the Halpha emission stars below the PMS locus (so-called BMS stars) are bona-fide members of NGC 2264 from their spatial distribution as well as from their near-IR excess in the 2 MASS color-color diagram. In addition, four objects around IRS-2 detected with the Spitzer IRAC are also classified as BMS stars. Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

New BMS Stars in NGC 2264 Strom. Fest Westward Look Resort April 4 -5,

New BMS Stars in NGC 2264 Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

Age Spread in NGC 2264? Strom. Fest Westward Look Resort April 4 -5, 2008

Age Spread in NGC 2264? Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

Photometric Variability as a Signpost of Youth • One of the characteristics of youth

Photometric Variability as a Signpost of Youth • One of the characteristics of youth used by the Strom’s in studying YSO’s in the 1970’s was photometric variability - particularly in the IR • One of Steve’s most recent papers was a chapter in the Spitzer Warm Mission workshop, where he advocated using IRAC for time series photometry in star-forming regions. • Steve’s paper was one impetus for Tom Soifer to request a DDT observation of a star-forming region to determine what could be learned from time series photometry with IRAC. Those data were obtained in early March - and this group is the first to see the results. Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

IC 1396 A - The Elephant Trunk Nebula Strom. Fest Westward Look Resort April

IC 1396 A - The Elephant Trunk Nebula Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

YSO’s in IC 1396 A Strom. Fest Westward Look Resort April 4 -5, 2008

YSO’s in IC 1396 A Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

Mid-IR Variability in IC 1396 A Strom. Fest Westward Look Resort April 4 -5,

Mid-IR Variability in IC 1396 A Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

Mid-IR Variability in IC 1396 A Strom. Fest Westward Look Resort April 4 -5,

Mid-IR Variability in IC 1396 A Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

Short-timescale Variability – a PMS Delta Scuti Star? Strom. Fest Westward Look Resort April

Short-timescale Variability – a PMS Delta Scuti Star? Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-

Conclusions • We are still arguing over some of the same issues raised in

Conclusions • We are still arguing over some of the same issues raised in Steve and Karen’s 1972 papers • We have made progress though – and Spitzer has served as a good tool to pursue this type of science Strom. Fest Westward Look Resort April 4 -5, 2008 JRS-