Young Star Clusters in the Dwarf Irregular Galaxy, UGC 7636, Interacting with the Giant Elliptical Galaxy NGC 4472

We present integrated Washington CT1 photometry of 18 bright blue objects discovered in the dwarf galaxy UGC 7636 which is located 5'.5 southeast of the giant elliptical galaxy NGC 4472, the brightest galaxy in the Virgo cluster. Several lines of evidence indicate that UGC 7636 is interacting violently with NGC 4472. These objects are very blue with colors of -0.4 < (C-T1) < 0.6, and their magnitudes are in the range of 20.6 < T1 < 22.9 mag which corresponds to absolute magnitudes of -10.6 < M(T1) < -8.3 mag for a distance modulus of (m-M)o = 31.2. These objects are grouped spatially in three regions: the central region of UGC 7636, the tidal tail region, and the HI cloud region. No such objects were found in the counter tail region. It is concluded that these objects are probably young star clusters which formed < 0.1Gyr ago during the interaction between UGC 7636 and NGC 4472. Surface photometry of UGC 7636 (r < 83") shows that there is a significant excess of blue light along the tidal tail region compared with other regions. The star clusters are bluer than the stellar light in the tidal tail region, indicating that these clusters might have formed later than most stars in the tidal tail region which were formed later than most stars in the main body of the galaxy.Comment: 18 pages (AASLaTeX), 6 Postscript figures, Accepted for publication in the Astronomical Journal, Nov. 30th, 199

Wide Field CCD Surface Photometry of the Giant Elliptical Galaxy NGC 4472 in the Virgo Cluster

We present deep wide field (16'.4 x 16'.4) Washington CT1 CCD surface photometry of the giant elliptical galaxy NGC 4472, the brightest member in the Virgo cluster. Our data cover a wider field than any previous CCD photometry as well as going deeper. Surface brightness profiles of NGC 4472 are not well fit by a single King model, but they can be fit approximately by two King models: with separate models for the inner and outer regions. Surface brightness profiles for the outer region can also be fit approximately by a deVaucouleurs law. There is clearly a negative color gradient within 3' of NGC 4472, in the sense that the color gets bluer with increasing radius. The slope of the color gradient for this region is derived to be $\Delta \mu (C-T_1)$ = -0.08 mag arcsec$^{-2}$ for $\Delta \log r =1$, which corresponds to a metallicity gradient of $\Delta$ [Fe/H] $= -0.2$ dex. However, the surface color gets redder slowly with increasing radius beyond 3'. A comparison of the structural parameters of NGC 4472 in C and T1 images has shown that there is little difference in the ellipse shapes between isochromes and isophotes. In addition, photometric and structural parameters of NGC 4472 have been determined.Comment: 8 pages(mnrasLaTeX), 8 Postscript figures, Accepted for publication in MNRAS, 2000

The Digital Disconnect: The Widening Gap Between Internet Savvy Students and Their Schools

Presents findings from a survey of public middle and high school students from thirty schools across the U.S. Looks at how students rely on the Internet to help them do their schoolwork, in addition to dozens of other education related tasks

Filamentary Star Formation: Observing the Evolution toward Flattened Envelopes

Filamentary structures are ubiquitous from large-scale molecular clouds (few parsecs) to small-scale circumstellar envelopes around Class 0 sources (~1000 AU to ~0.1 pc). In particular, recent observations with the Herschel Space Observatory emphasize the importance of large-scale filaments (few parsecs) and star formation. The small-scale flattened envelopes around Class 0 sources are reminiscent of the large-scale filaments. We propose an observationally derived scenario for filamentary star formation that describes the evolution of filaments as part of the process for formation of cores and circumstellar envelopes. If such a scenario is correct, small-scale filamentary structures (0.1 pc in length) with higher densities embedded in starless cores should exist, although to date almost all the interferometers have failed to observe such structures. We perform synthetic observations of filaments at the prestellar stage by modeling the known Class 0 flattened envelope in L1157 using both the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and the Atacama Large Millimeter/Submillimeter Array (ALMA). We show that with reasonable estimates for the column density through the flattened envelope, the CARMA D-array at 3mm wavelengths is not able to detect such filamentary structure, so previous studies would not have detected them. However, the substructures may be detected with CARMA D+E array at 3 mm and CARMA E array at 1 mm as a result of more appropriate resolution and sensitivity. ALMA is also capable of detecting the substructures and showing the structures in detail compared to the CARMA results with its unprecedented sensitivity. Such detection will confirm the new proposed paradigm of non-spherical star formation.Comment: 9 pages, 10 figures. Accepted by Ap

Dwyer Google Migration

The IT staff at Dwyer Instruments encountered several issues when switching to use Google’s business technology services. These problems included lack of a button to open a new email draft with a PDF already attached, the timestamp function in Google Sheets displaying the current time instead of the time it was entered, duplicate Google Sheets spreadsheets not maintaining protected ranges, lack of a timeline chart in Google Sheets, inability to save Gmail searches, lack of event templates in Google Calendar, and lack of a workflow management tool in Google’s business technology suite. On site personnel were asked to communicate what would help smooth the transition to the G Suite. One challenge encountered was the difficulty in publishing G-Suite add-ons to Google’s online marketplace. Another challenge is presented by the lack of examples of G-Suite add-ons. This makes it tough to create add-ons since there are few resources to go off of. A G-Suite add-on was developed to create an in-page side window in Gmail and Drive to allow attachments from selected conversations or Drive files to be attached and sent with an email. A Google Sheets add-on was also developed in order to insert the current time into a selected cell. While some needs remain outstanding, but the project made significant progress toward solving some of their IT issues

Viscous diffusion and photoevaporation of stellar disks

The evolution of a stellar disk under the influence of viscous evolution, photoevaporation from the central source, and photoevaporation by external stars is studied. We take the typical parameters of TTSs and the Trapezium Cluster conditions. The photoionizing flux from the central source is assumed to arise both from the quiescent star and accretion shocks at the base of stellar magnetospheric columns, along which material from the disk accretes. The accretion flux is calculated self-consistently from the accretion mass loss rate. We find that the disk cannot be entirely removed using only viscous evolution and photoionization from the disk-star accretion shock. However, when FUV photoevaporation by external massive stars is included the disk is removed in 10^6 -10^7yr; and when EUV photoevaporation by external massive stars is included the disk is removed in 10^5 - 10^6yr. An intriguing feature of photoevaporation by the central star is the formation of a gap in the disk at late stages of the disk evolution. As the gap starts forming, viscous spreading and photoevaporation work in resonance. There is no gap formation for disks nearby external massive stars because the outer annuli are quickly removed by the dominant EUV flux. On the other hand, at larger, more typical distances (d>>0.03pc) from the external stars the flux is FUV dominated. As a consequence, the disk is efficiently evaporated at two different locations; forming a gap during the last stages of the disk evolution.Comment: 27 pages, 11 figures, accepted for publication in Ap