MESAS: Measuring the Emission of Stellar Atmospheres at Submm/mm wavelengths

In the early stages of planet formation, small dust grains grow to become mm sized particles in debris disks around stars. These disks can in principle be characterized by their emission at submillimeter and millimeter wavelengths. Determining both the occurrence and abundance of debris in unresolved circumstellar disks of A-type main-sequence stars requires that the stellar photospheric emission be accurately modeled. To better constrain the photospheric emission for such systems, we present observations of Sirius A, an A-type star with no known debris, from the JCMT, SMA, and VLA at 0.45, 0.85, 0.88, 1.3, 6.7, and 9.0 mm. We use these observations to inform a PHOENIX model of Sirius A's atmosphere. We find the model provides a good match to these data and can be used as a template for the submm/mm emission of other early A-type stars where unresolved debris may be present. The observations are part of an ongoing observational campaign entitled Measuring the Emission of Stellar Atmospheres at Submm/mm wavelengths (MESAS)Comment: 17 pages, 1 figure, Accepted to AJ on April 25th 201

Constraining the Radio Emission of TRAPPIST-1

TRAPPIST-1 is an ultracool dwarf (UCD) with a system of 7 terrestrial planets, at least three of which orbit in the habitable zone. The radio emission of such low-mass stars is poorly understood; few UCDs have been detected at radio frequencies at all, and the likelihood of detection is only loosely correlated with stellar properties. Relative to other low-mass stars, UCDs with slow rotation such as TRAPPIST-1 tend to be radio dim, whereas rapidly rotating UCDs tend to have strong radio emission - although this is not always the case. We present radio observations of TRAPPIST-1 using ALMA at 97.5 GHz and the VLA at 44 GHz. TRAPPIST-1 was not detected at either frequency and we place $3 \sigma$ upper flux limits of 10.6 and 16.2 $\mu$Jy, respectively. We use our results to constrain the magnetic properties and possible outgoing high energy particle radiation from the star. The presence of radio emission from UCDs is indicative of a stellar environment that could pose a threat to life on surrounding planets. Gyrosynchrotron emission, discernible at frequencies between 20 and 100 GHz, is one of the only processes that can be used to infer the presence of high energy particles released during magnetic reconnection events. Since M dwarfs are frequent hosts of terrestrial planets, characterizing their stellar emission is a crucial part of assessing habitability. Exposure to outgoing high energy particle radiation - traceable by radio flux - can erode planetary atmospheres. While our results do not imply that the TRAPPIST-1 planets are suitable for life, we find no evidence that they are overtly unsuitable due to proton fluxes.Comment: 9 pages, 3 figures, accepted to Ap

Period and chemical evolution of SC stars

The SC and CS stars are thermal-pulsing AGB stars with C/O ratio close to unity. Within this small group, the Mira variable BH Cru recently evolved from spectral type SC (showing ZrO bands) to CS (showing weak C2). Wavelet analysis shows that the spectral evolution was accompanied by a dramatic period increase, from 420 to 540 days, indicating an expanding radius. The pulsation amplitude also increased. Old photographic plates are used to establish that the period before 1940 was around 490 days. Chemical models indicate that the spectral changes were caused by a decrease in stellar temperature, related to the increasing radius. There is no evidence for a change in C/O ratio. The evolution in BH Cru is unlikely to be related to an on-going thermal pulse. Periods of the other SC and CS stars, including nine new periods, are determined. A second SC star, LX Cyg, also shows evidence for a large increase in period, and one further star shows a period inconsistent with a previous determination. Mira periods may be intrinsically unstable for C/O ~ 1; possibly because of a feedback between the molecular opacities, pulsation amplitude, and period. LRS spectra of 6 SC stars suggest a feature at wavelength > 15 micron, which resembles one recently attributed to the iron-sulfide troilite. Chemical models predict a large abundance of FeS in SC stars, in agreement with the proposed association.Comment: 14 pages, 20 figures. MNRAS, 2004, accepted for publication. Janet Mattei, one of the authors, died on 22 March, 2004. This paper is dedicated to her memor

The Vehicle, Fall 2010

Table of ContentsPoetryFill Your Mouth with BerriesAaron Whitepage 1 RelationsJamie Van Allenpage 2 ExodusMegan Marie Olsonpage 4 Single FileRashelle McNairpage 7 The Aesthetic Value of the Moon, by CandlelightKathy Deckerpage 15 FactalsGabrielle Keigherpage 16 Day 5David Jacksonpage 17 Esta LloviendoHeather Gerrishpage 19 FacebrokeDarrin Gordonpage 23 5:08 pmNikki Riechertpage 24 Train TunnelsAshton Tembypage 34 VariationsKathy Deckerpage 35 WantRashelle McNairpage 36 FriendshipScott Maypage 37 Golden LandJacob Swansonpage 38 Last Night I DreamtAshton Tembypage 39 Smallest GestureScott Maypage 44 Somebody\u27s Hut in MexicoGinamarie Lobiancopage 45 Some Things You Just Can\u27t Tap Dance AroundClint Walkerpage 53 Prose Lamparus de DiosAaron Whitepage 8 Learning CurveScott Maypage 18 RocktonKatelyn Pfaffpage 20 Fatal DistractionSolomohn Ennispage 25 Noodle NonsenseGabrielle Keigherpage 41 AntarcticaMichael Payeapage 46 Special Features James K Johnson Award Winners: God is GraciousJohn Klyczekpage 57 To My Ever Growing ChestJennifer Hindespage 74 God\u27s ScapegoatJennifer Hindespage 76 Rape (Verb, Noun)Jennifer Hindespage 78 Featured Artist: Ashton Tembypage 81 Editor\u27s Pick: The Shooter by Patrick Hallpage 87 Chapbook 2010 Author:Kim Hunter-Perkinspage 114 About the Contributorspage 118 About the Editorspage 122https://thekeep.eiu.edu/vehicle/1092/thumbnail.jp

The Vehicle, Fall 2010

Table of ContentsPoetryFill Your Mouth with BerriesAaron Whitepage 1 RelationsJamie Van Allenpage 2 ExodusMegan Marie Olsonpage 4 Single FileRashelle McNairpage 7 The Aesthetic Value of the Moon, by CandlelightKathy Deckerpage 15 FactalsGabrielle Keigherpage 16 Day 5David Jacksonpage 17 Esta LloviendoHeather Gerrishpage 19 FacebrokeDarrin Gordonpage 23 5:08 pmNikki Riechertpage 24 Train TunnelsAshton Tembypage 34 VariationsKathy Deckerpage 35 WantRashelle McNairpage 36 FriendshipScott Maypage 37 Golden LandJacob Swansonpage 38 Last Night I DreamtAshton Tembypage 39 Smallest GestureScott Maypage 44 Somebody\u27s Hut in MexicoGinamarie Lobiancopage 45 Some Things You Just Can\u27t Tap Dance AroundClint Walkerpage 53 Prose Lamparus de DiosAaron Whitepage 8 Learning CurveScott Maypage 18 RocktonKatelyn Pfaffpage 20 Fatal DistractionSolomohn Ennispage 25 Noodle NonsenseGabrielle Keigherpage 41 AntarcticaMichael Payeapage 46 Special Features James K Johnson Award Winners: God is GraciousJohn Klyczekpage 57 To My Ever Growing ChestJennifer Hindespage 74 God\u27s ScapegoatJennifer Hindespage 76 Rape (Verb, Noun)Jennifer Hindespage 78 Featured Artist: Ashton Tembypage 81 Editor\u27s Pick: The Shooter by Patrick Hallpage 87 Chapbook 2010 Author:Kim Hunter-Perkinspage 114 About the Contributorspage 118 About the Editorspage 122https://thekeep.eiu.edu/vehicle/1092/thumbnail.jp