Mercedes Gomez

Ubvri light curves of 44 type ia supernovae

We present UBVRI photometry of 44 Type Ia supernovae (SNe Ia) observed from 1997 to 2001 as part of a continuing monitoring campaign at the Fred Lawrence Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics. The data set comprises 2190 observations and is the largest homogeneously observed and reduced sample of SNe Ia to date, nearly doubling the number of well-observed, nearby SNe Ia with published multicolor CCD light curves. The large sample of U-band photometry is a unique addition, with important connections to SNe Ia observed at high redshift. The decline rate of SN Ia U-band light curves correlates well with the decline rate in other bands, as does the U - B color at maximum light. However, the U-band peak magnitudes show an increased dispersion relative to other bands even after accounting for extinction and decline rate, amounting to an additional ~40% intrinsic scatter compared to the B band.

On the spatial distribution of pre-main-sequence stars in Taurus

We derive characteristic properties of the nonrandom spatial distribution of pre-main-sequence stars in the Taurus-Auriga molecular cloud by applying several different statistical techniques. We find that a power-law form for the two-point angular correlation function (with index −1.2) reproduces the overall shape of the actual pre-main-sequence distribution in Taurus at small angular scales (∼0.3°). This result is consistent with the existence of real clustering in the T Tauri distribution. With the aid of the nearest-neighbor distribution technique, we determine a median projected separation of −0.3 pc for young stars in this cloud, even after eliminating close pairs with separations less than 20″ (−3000 AU at the distance of Taurus) from our sample

The embedded young stars in the Taurus-Auriga molecular cloud. II - Models for scattered light images

We describe NIR imaging observations of embedded young stars in the Taurus-Auriga molecular cloud. We find a large range in J-K and H-K colors for these class I sources. The bluest objects have colors similar to the reddest T Tauri stars in the cloud; redder objects lie slightly above the reddening line for standard ISM dust and have apparent K extinctions of up to 5 mag. Most of these sources also show extended NIR emission on scales of 10-20 arcsec which corresponds to linear sizes of 1500-3000 AU. The NIR colors and nebular morphologies for this sample and the magnitude of linear polarization in several sources suggest scattered light produces most of the NIR emission in these objects. We present modeling results that suggest mass infall rates that agree with predictions for cold clouds and are generally consistent with rates estimated from radiative equilibrium models. For reasonable dust grain parameters, the range of colors and extinctions require flattened density distributions with polar cavities evacuated by bipolar outflows. These results support the idea that infall and outflow occur simultaneously in deeply embedded bipolar outflow sources. The data also indicate fairly large centrifugal radii and large inclinations to the rotational axis for a typical source.

A Near-Infrared Imaging Survey of the Chamaeleon I Dark Cloud

We describe a near-infrared imaging survey covering ~1 deg2 of the Chamaeleon I dark cloud. The survey is complete for K < 15.0, H < 16.0, and J < 16.5, roughly 2 magnitudes more sensitive than previous large-scale surveys. We use the large number of background stars detected to derive an accurate near-infrared extinction law for the cloud and select new candidate members with near-infrared color excesses. We list ~100 candidates of the cloud with K ≥ 12.0, based on their positions in the J-H, H-K color-color diagram. These new stars have low luminosities (K ~ 12–16, H-K 0.5–1.5) and may have masses close to or even below the hydrogen-burning limit.

A 3 μm Survey of the Chamaeleon I Dark Cloud

We describe an L-band photometric survey of ~ 0.5 deg2 of the Chamaeleon I dark cloud. The survey has a completeness limit of L < 11.0. Our survey detects 124 sources, including all known pre–main-sequence stars with L ≤ 11. The fraction of sources with near-IR excess emission is 58% ± 4% for K = 9–11. Cha I sources have bluer H-K and K-L colors than pre–main-sequence stars in Taurus-Auriga. These sources also have a strong correlation between EW(Hα) and K-L. Stars with K-L≤ 0.6 have weak Hα emission; stars with K-L≥ 0.6 have strong Hα emission. Because many Cha I sources are heavily reddened, this division between weak emission T Tauri stars and classical T Tauri stars occurs at a redder K-L than in Taurus-Auriga.

A Three Micron Survey of the Chamaeleon I Dark Cloud

We describe an L-band photometric survey of ~ 0.5 deg2 of the Chamaeleon I dark cloud. The survey has a completeness limit of L < 11.0. Our survey detects 124 sources, including all known pre–main-sequence stars with L ≤ 11. The fraction of sources with near-IR excess emission is 58% ± 4% for K = 9–11. Cha I sources have bluer H-K and K-L colors than pre–main-sequence stars in Taurus-Auriga. These sources also have a strong correlation between EW(Hα) and K-L. Stars with K-L≤ 0.6 have weak Hα emission; stars with K-L≥ 0.6 have strong Hα emission. Because many Cha I sources are heavily reddened, this division between weak emission T Tauri stars and classical T Tauri stars occurs at a redder K-L than in Taurus-Auriga.

First results of the CIDA Schmidt survey: selected zones in Taurus-Auriga

We have begun an objective-prism H-alpha survey of star-forming regions using the CIDA 1 m Schmidt Camera, with a limiting magnitude of V ~ 18. We report here first results for selected areas of the Taurus-Auriga molecular clouds. Of the list of candidates found in the objective-prism plates, 12 stars have been confirmed as pre-main sequence by the detection of the Li I 6707 A absorption line. Five of these stars are in the dark cloud L1544, where only one T Tauri star was previously known. The new stars have very late spectral types and most have estimated masses between 0.2 M and 0.3 M.

On the ages of pre-main-sequence stars in Taurus

A search for pre-main-sequence stars in a region of about 12.7 deg 2 near the L 1551 complex in the Taurus molecular cloud have been made. Only two new pre-main-sequence stars have been identified from optical spectra of 383 proper motion candidates on the basis of Li I 6707 A absorption. These stars have ages of ∼4 × 10 6 yr; no evidence are found for a large number of pre-main-sequence stars with ages comparable to the crossing time of the cloud (∼ 10 7 yr)

Sub-arcsec resolution near-infrared images of the Cederblad 110 region ?

We present the results of deep (Ks =1 8:9) sub-arcsec resolution (0.3 00 ) imaging observations of the Cederblad 110 region in the Chamaeleon I dark cloud. This region (roughly 5 0 5 0 ) is characterized by the presence of six ISOCAM-detected young stellar objects (YSOs). Our images have recovered all these sources at near-infrared (near-IR) wavelengths. Ced 110 IRS4, the brightest object in the region, is associated with a remarkable near-IR bipolar nebulosity. Ced 110 IRS6 is resolved in a double system IRS6a and IRS6b with a separation of 2 00 (320 AU at the distance of the Cha I cloud). We have combined 1.3 mm, far and mid-IR fluxes from the literature with our JHK data and obtained the spectral energy distributions (SEDs) for three (IRS4, IRS6a and ISO-ChaI86) of the six ISOCAM sources in the region. We modelled the SEDs of IRS6a and ISO-ChaI86 with a spherically symmetric dusty envelope, using the DUSTY code. These objects are clear Class I sources of the cloud. Finally, we report the detection of three new objects in this region (NIR 72, 84 and 89) with signicant near-IR excess. If these sources are associated with the cloud, the derived luminosities and masses suggest that they are candidate young brown dwarfs of Chamaeleon I.

A Near-Infrared Imaging Survey of Coalsack Globule 2

We describe a near-infrared imaging survey of Globule 2 in the Coalsack. This Bok globule is the highest-density region of this southern hemisphere molecular cloud and is the most likely location for young stars in this complex. The survey is complete for K < 14.0, H < 14.5, and J < 15.5, several magnitudes more sensitive than previous observations of this globule. From the large number of background stars, we derive an accurate near-infrared extinction law for the cloud. Our result, EJ-H/EH-K = 2.08 ± 0.03, is significantly steeper than results for other southern clouds. We use the J-H/H-K color-color diagram to identify two potential young stars with K < 14.0 in the region. We apply H-band star counts to derive the density profile of Coalsack Globule 2 and use a polytropic model to describe the internal structure of this small cloud. For a gas temperature T ~ 15 K, this globule is moderately unstable.